Imaging device

ABSTRACT

An imaging device according to the present disclosure includes: a photoelectric converter that generates signal charge; a semiconductor substrate including a first semiconductor layer containing an impurity of a first conductivity type and an impurity of a second conductivity type; and a first transistor including a first impurity region of the second conductivity type in the first semiconductor layer. The first semiconductor layer includes: a charge accumulation region of the second conductivity type, for accumulating the signal charge; and a blocking structure between the charge accumulation region and the first transistor. The blocking structure includes a second impurity region of the first conductivity type, a third impurity region of the second conductivity type, and a fourth impurity region of the first conductivity type, which are arranged in that order in a direction from the first impurity region toward the charge accumulation region, at the surface of the first semiconductor layer.

BACKGROUND 1. Technical Field

The present disclosure relates to an imaging device.

2. Description of the Related Art

Charge-coupled device (CCD) image sensors and complementary metal-oxidesemiconductor (CMOS) image sensors are in widespread use in digitalcameras and the like. These image sensors have photodiodes formed on asemiconductor substrate, which is a well-known fact.

A structure is being proposed where a photoelectric conversion layer isdisposed above the semiconductor substrate instead of the photodiodes,as disclosed in International Publication Nos. 2014/002330 and2012/147302, for example. Imaging device that have this sort ofstructure may be referred to as stacked imaging devices. In a stackedimaging device, charges generated by photoelectric conversion aretemporarily accumulated in diffusion regions and the like formed in thesemiconductor substrate, as signal charges. Signals corresponding to theamount of charges accumulated are read out via a CCD circuit or CMOScircuit formed on the semiconductor substrate.

SUMMARY

If charges that are different from signal charges expressing an imageflow into diffusion regions temporarily storing signals charges, thiscan lead to noise. Noise causes deterioration of the obtained image. Itis advantageous to be able to suppress unintended movement of charges.Hereinafter, such unintended movement of charges may be referred to as aleak current.

One non-limiting and exemplary embodiment provides the following.

In one general aspect, the techniques disclosed here feature an imagingdevice, including: a photoelectric converter that generates a signalcharge by photoelectric conversion of light; a semiconductor substratethat includes a first semiconductor layer containing an impurity of afirst conductivity type and an impurity of a second conductivity typedifferent from the first conductivity type; and a first transistor thatincludes, as a source or a drain, a first impurity region of the secondconductivity type in the first semiconductor layer, wherein the firstsemiconductor layer includes: a charge accumulation region that is animpurity region of the second conductivity type, the charge accumulationregion being configured to accumulate the signal charge; and a blockingstructure that is located between the charge accumulation region and thefirst transistor, the blocking structure includes: a second impurityregion of the first conductivity type, a third impurity region of thesecond conductivity type, and a fourth impurity region of the firstconductivity type, and at the surface of the first semiconductor layer,the second impurity region, the third impurity region, and the fourthimpurity region, are arranged in that order in a first direction fromthe first impurity region toward the charge accumulation region.

It should be noted that general or specific embodiments may beimplemented as an element, a device, a module, system, or a method.General or specific embodiments may be implemented as any selectivecombination of element, device, module, system, and method.

Additional benefits and advantages of the disclosed embodiments willbecome apparent from the specification and drawings. The benefits and/oradvantages may be individually obtained by the various embodiments andfeatures of the specification and drawings, which need not all beprovided in order to obtain one or more of such benefits and/oradvantages.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an exemplary circuit configuration ofan imaging device according to a first embodiment of the presentdisclosure;

FIG. 2 is a schematic diagram illustrating an exemplary configuration ofan imaging device according to the first embodiment of the presentdisclosure;

FIG. 3A is a cross-sectional diagram schematically illustrating anexample of a device structure of a first pixel illustrated in FIG. 2;

FIG. 3B is a cross-sectional diagram schematically illustrating a devicestructure of an imaging device according to a first modification of thefirst embodiment;

FIG. 4 is a diagram illustrating an exemplary configuration of animaging device according to a second modification of the firstembodiment;

FIG. 5 is a cross-sectional diagram schematically illustrating a devicestructure of a pixel that an imaging device according to the secondmodification of the first embodiment has;

FIG. 6A is a diagram schematically illustrating an example of electricalconnection between a second pixel and a voltage supply circuit;

FIG. 6B is a diagram schematically illustrating another example ofelectrical connection between the second pixel and the voltage supplycircuit;

FIG. 7 is a diagram schematically illustrating yet another example ofelectrical connection as to a shielding structure;

FIG. 8 is a schematic diagram illustrating the circuit configuration ofa third modification of the imaging device according to the firstembodiment;

FIG. 9 is a cross-sectional diagram schematically illustrating anexample of the device structure of a third pixel illustrated in FIG. 8;

FIG. 10 is a schematic plan view illustrating an example of a layout ofelements in the third pixel;

FIG. 11 is a schematic plan view illustrating an example of atwo-dimensional array of the third pixels illustrated in FIG. 10;

FIG. 12 is a schematic plan view illustrating another example of atwo-dimensional array of the third pixels;

FIG. 13 is a schematic diagram illustrating the circuit configuration ofa fourth modification of the imaging device according to the firstembodiment of the present disclosure;

FIG. 14 is a schematic plan view illustrating an example of the layoutof elements in the fourth pixel illustrated in FIG. 13;

FIG. 15 is a schematic plan view illustrating an example of atwo-dimensional array of the fourth pixels illustrated in FIG. 13;

FIG. 16A is a cross-sectional view schematically illustrating anexemplary device structure of a pixel that the imaging device accordingto a second embodiment of the present disclosure has;

FIG. 16B is a cross-sectional view schematically illustrating the devicestructure of a pixel that the imaging device according to a firstmodification of the second embodiment of the present disclosure has;

FIG. 17 is a cross-sectional view schematically illustrating the devicestructure of a pixel that the imaging device according to a secondmodification of the second embodiment of the present disclosure has;

FIG. 18 is a diagram schematically illustrating an example of electricalconnection between a fifth pixel and a voltage supply circuit;

FIG. 19 is a schematic plan view illustrating an example of a layout ofelements in a sixth pixel that an imaging device according to a thirdembodiment of the present disclosure has;

FIG. 20 is a diagram illustrating an exemplary circuit configuration ofthe sixth pixel illustrated in FIG. 19;

FIG. 21 is a schematic diagram for describing a model used forsimulation;

FIG. 22 is a diagram illustrating simulation results relating to a firstexample assuming basically the same structure as the fifth pixelillustrated in FIG. 5, illustrating calculation results regardingpotential at each portion;

FIG. 23 is a diagram illustrating simulation results relating to thefirst example assuming basically the same structure as the fifth pixelillustrated in FIG. 5, illustrating calculation results regardingcurrent density at each portion;

FIG. 24 is a diagram illustrating calculation results relating topotential at each portion in a sample of a second example;

FIG. 25 is a diagram illustrating calculation results relating tocurrent density at each portion in a sample of the second example;

FIG. 26 is a diagram illustrating calculation results relating topotential at each portion in a sample of a first comparative example;

FIG. 27 is a diagram illustrating calculation results relating tocurrent density at each portion in a sample of the first comparativeexample;

FIG. 28 is a diagram illustrating calculation results regarding theproportion of charge flowing into a charge accumulation region, out ofcharges generated nearby an n-type impurity region;

FIG. 29 is a diagram illustrating calculation results relating toelectric field at each portion in a sample of the first example; and

FIG. 30 is a diagram illustrating calculation results relating toelectric field at each portion in a sample of the second example.

DETAILED DESCRIPTION

Aspects of the present disclosure are as described below.

Item 1

An imaging device, including:

a photoelectric converter that generates a signal charge byphotoelectric conversion of light;

a semiconductor substrate that includes a first semiconductor layercontaining an impurity of a first conductivity type and an impurity of asecond conductivity type different from the first conductivity type; and

a first transistor that includes, as a source or a drain, a firstimpurity region of the second conductivity type in the firstsemiconductor layer, wherein

the first semiconductor layer includes:

-   -   a charge accumulation region that is an impurity region of the        second conductivity type, the charge accumulation region being        configured to accumulate the signal charge; and    -   a blocking structure that is located between the charge        accumulation region and the first transistor,

the blocking structure includes:

-   -   a second impurity region of the first conductivity type,    -   a third impurity region of the second conductivity type, and    -   a fourth impurity region of the first conductivity type, and

at the surface of the first semiconductor layer, the second impurityregion, the third impurity region, and the fourth impurity region, arearranged in that order in a first direction from the first impurityregion toward the charge accumulation region.

Item 2

The imaging device according to Item 1, wherein

the semiconductor substrate includes

-   -   a supporting substrate including an impurity of the first        conductivity type, and    -   a second semiconductor layer that is located between the        supporting substrate and the first semiconductor layer, the        second semiconductor layer including an impurity of the second        conductivity type.        Item 3

The imaging device according to Item 2, wherein

the semiconductor substrate further includes a third semiconductor layerthat is located between the first semiconductor layer and the secondsemiconductor layer, the third semiconductor layer including an impurityof the first conductivity type,

the third semiconductor layer has an opening that overlaps the thirdimpurity region in a plan view, and

a concentration of impurity of the first conductivity type in a regionlocated in the opening is lower than a concentration of impurity of thefirst conductivity type in the third semiconductor layer.

Item 4

The imaging device according to any one of Items 1 through 3, furthercomprising a voltage supply circuit configured to apply, to the thirdimpurity region, a first voltage that is inverse bias with regard to thefirst semiconductor layer, or a second voltage that is a same voltage asthe first semiconductor layer, in a period in which the signal charge isaccumulated in the charge accumulation region.

Item 5

The imaging device according to Item 4, wherein a third voltage that isdifferent from the first voltage, or the second voltage that is 0 V, isapplied to the second impurity region and the fourth impurity region viathe first semiconductor layer, in the period.

Item 6

The imaging device according to Item 5, wherein the third voltage isless than the first voltage.

Item 7

The imaging device according to any one of Items 4 through 6, wherein asame voltage is applied to the third impurity region and the secondsemiconductor layer in the period.

Item 8

The imaging device according to any one of Items 1 through 7, furthercomprising:

a second transistor including the charge accumulation region as one of asource and a drain, wherein

a same voltage is applied to the third impurity region and the other ofthe source and the drain of the second transistor.

Item 9

The imaging device according to any one of Items 1 through 8, whereinthe second impurity region and the fourth impurity region are a singlecontinuous impurity region surrounding the third impurity region.

Item 10

An imaging device, comprising:

a photoelectric converter that generates a signal charge byphotoelectric conversion of light;

a semiconductor substrate that includes a first semiconductor layercontaining an impurity of a first conductivity type and an impurity of asecond conductivity type different from the first conductivity type; and

a first transistor that includes, as a source or a drain, a firstimpurity region of the second conductivity type in the firstsemiconductor layer, wherein

the first semiconductor layer includes:

-   -   a charge accumulation region that is an impurity region of the        second conductivity type, the charge accumulation region being        configured to accumulate the signal charge; and    -   a blocking structure that is located between the charge        accumulation region and the first transistor, and

the blocking structure includes:

-   -   a second impurity region of the first conductivity type; and    -   a third impurity region of the first conductivity type, that is        located in the second impurity region, a part of the third        impurity region being located on the surface of the first        semiconductor layer, a concentration of impurity of the first        conductivity type in the third impurity region being higher than        a concentration of impurity of the first conductivity type in        the second impurity region.        Item 11

The imaging device according to Item 10, wherein

the semiconductor substrate includes

-   -   a supporting substrate including an impurity of the first        conductivity type, and    -   a second semiconductor layer that is located between the        supporting substrate and the first semiconductor layer, the        second semiconductor layer including an impurity of the second        conductivity type.        Item 12

The imaging device according to Item 11, wherein

the semiconductor substrate further includes a fourth impurity regionthat is located between the first semiconductor layer and the secondsemiconductor layer, the fourth impurity region including an impurity ofthe first conductivity type, and

a concentration of impurity of the first conductivity type in the fourthimpurity region is higher than a concentration of impurity of the firstconductivity type in the first semiconductor layer.

Item 13

The imaging device according to Item 12, wherein the fourth impurityregion does not overlap the first impurity region in a plan view.

Item 14

The imaging device according to either Item 12 or 13, furthercomprising:

a second transistor including the charge accumulation region as one of asource and drain, wherein

the fourth impurity region does not overlap the other of the source andthe drain of the second transistor in a plan view.

Item 15

The imaging device according to any one of Items 10 through 14, furthercomprising: a voltage supply circuit configured to apply a first voltageto the third impurity region, in a period in which the signal charge isaccumulated in the charge accumulation region.

Item 16

The imaging device according to Item 15, wherein a same voltage as thefirst voltage is applied to the second impurity region via thesupporting substrate.

Item 17

An imaging device including or more pixels, wherein

each of the one or more pixels includes

-   -   a photoelectric converter,    -   a semiconductor substrate having a first impurity region of a        second conductivity type, and a charge accumulation region of        the second conductivity type that is electrically connected to        the photoelectric converter,    -   a first transistor that has a gate electrically connected to the        photoelectric converter, and that includes a first impurity        region as one of a source and drain, and    -   a second transistor that has the charge accumulation region as        one of a source and drain,

the semiconductor substrate further includes

-   -   a second impurity region and fourth impurity region of a first        conductivity type disposed in the semiconductor substrate in a        manner separated from each other between the first impurity        region and the charge accumulation region, and    -   a third impurity region of the second conductivity type that is        located between the second impurity region and the fourth        impurity region, and

at least part of the third impurity region is located on the surface ofthe semiconductor substrate.

According to the configuration of Item 17, the second and fourthimpurity regions of the first conductivity type are provided between thefirst impurity region of the second conductivity type and the chargeaccumulation region, and further, the third impurity region of thesecond conductivity type is provided between these. Accordingly, chargesgenerated at the p-n junction of the first impurity region and movingtoward the charge accumulation region can be collected by potentialgradient by the third impurity region before reaching the chargeaccumulation region. That is to say, contamination of the chargeaccumulation region by excess charges can be suppressed, anddeterioration of the image due to leak current can be suppressed.

Item 18

The imaging device according to Item 17, wherein

the semiconductor substrate includes

-   -   a supporting substrate including an impurity of the first        conductivity type,    -   a first semiconductor layer that is located above the supporting        substrate and that includes an impurity of the first        conductivity type, and    -   a second semiconductor layer that is located between the        supporting substrate and the first semiconductor layer, and that        includes an impurity of the second conductivity type, and

the charge accumulation region, first impurity region, second impurityregion, fourth impurity region, and third impurity region are located inthe first semiconductor layer.

According to the configuration of Item 18, a region with relatively lowconcentration of impurity can be disposed in the periphery a positionwhere a contact plug having electrical connection with the photoelectricconverter is in contact with the semiconductor substrate. Accordingly,the intensity of electric field at the p-n junction formed between thecharge accumulation region and the periphery thereof can be reduced, forexample.

Item 19

The imaging device according to Item 18, wherein

the semiconductor substrate further includes a third semiconductor layerthat is located between the first semiconductor layer and the secondsemiconductor layer, and that includes an impurity of the firstconductivity type,

the third semiconductor layer is formed at a region other than a regiondirectly beneath the third impurity region, and

the concentration of impurity of the portion located directly beneaththe third impurity region in the first semiconductor layer is lower thanthat of the third semiconductor layer.

According to the configuration of Item 19, the position of the p-njunction formed between the second semiconductor layer and the peripherythereof bulges toward the third impurity region directly beneath thethird impurity region, so the movement path of changes heading from thefirst impurity region toward the charge accumulation region is narrowed.Accordingly, even if charges that are generated at the p-n junction ofthe first impurity region and the periphery thereof and that movethrough the semiconductor substrate are generated, such charges advancetoward the third impurity region or the second semiconductor layerfollowing the potential gradient. As a result, movement of minoritycarriers to the charge accumulation region is suppressed moreeffectively.

Item 20

The imaging device according to either Item 18 or 19, further including:

a voltage supply circuit that applies a first voltage that is inversebias with regard to the first semiconductor layer, or a second voltageof 0 V that is equipotential with the first semiconductor layer, to thethird impurity region, in at least a period in which charges generatedby the photoelectric converter are accumulated in the chargeaccumulation region more efficiently.

According to the configuration of Item 20, external voltage can beapplied to the third impurity region, so excess charges moving towardthe charge accumulation region can be recovered by the third impurityregion.

Item 21

The imaging device according to Item 20, wherein the second impurityregion and the fourth impurity region receive supply of a third voltagethat differs from the first voltage or the second voltage of 0 V via thefirst semiconductor layer, in the charge accumulation period.

Item 22

The imaging device according to Item 21, wherein the third voltage islower than the first voltage.

According to the configuration of Item 22, movement of minority carriersthat are the cause of leak current to the charge accumulation region canbe suppressed even more efficiently.

Item 23

The imaging device according to any one of Items 20 through 22, whereinthe second semiconductor layer receives supply of voltage that is incommon with the first voltage or second voltage, in the chargeaccumulation period.

Item 24

The imaging device according to any one of Items 17 through 23, whereincommon voltage is applied to the third impurity region and the other ofthe source and drain of the second transistor.

According to the configuration of Item 24, the voltage supplied to theblocking structure that includes the third impurity region as a partthereof, and the reset voltage supplied to the second transistor can bemade to be in common, so there is no need to provide a reset voltagesource separately, which is advantageous in reduction of size of theimaging device.

Item 25

An imaging device including one or more pixels, wherein

each of the one or more pixels includes

-   -   a photoelectric converter,    -   a semiconductor substrate having a first impurity region of a        second conductivity type, and a charge accumulation region of        the second conductivity type that is electrically connected to        the photoelectric converter,    -   a first transistor that has a gate electrically connected to the        photoelectric converter, and that includes a first impurity        region as one of a source and drain, and    -   a second transistor that has the charge accumulation region as        one of a source and drain,

the semiconductor substrate further includes

-   -   a second impurity region of a first conductivity type that is        located between the first impurity region and the charge        accumulation region, and    -   a third impurity region of the first conductivity type that is        located in the second impurity region, and that has a higher        concentration of impurity than the second impurity region, and

at least part of the third impurity region is located on the surface ofthe semiconductor substrate.

According to the configuration of Item 25, effects the same as Item 17can be obtained. Further, the conductivity type is held in commonbetween the second impurity region and the third impurity region, whichreduces the number of p-n junctions in the semiconductor substrate, soeffects of reducing the occurrence of charges that cause leak currentcan be anticipated.

Item 26

The imaging device according to Item 25, wherein

the semiconductor substrate includes

-   -   a supporting substrate including an impurity of the first        conductivity type,    -   a first semiconductor layer that is located above the supporting        substrate and that includes an impurity of the first        conductivity type, and    -   a second semiconductor layer that is located between the        supporting substrate and the first semiconductor layer, and that        includes an impurity of the second conductivity type, and

the charge accumulation region, the first impurity region, and thesecond impurity region are located in the first semiconductor layer.

According to the configuration of Item 26, effects the same as Item 18can be obtained.

Item 27

The imaging device according to Item 26, wherein

the semiconductor substrate is located on the second semiconductorlayer, and further includes a fourth impurity region that includesimpurity of the first conductivity type, and

the concentration of impurity of the fourth impurity region is higherthan that of the first semiconductor layer.

Item 28

The imaging device according to Item 27, wherein the fourth impurityregion is not located directly beneath the first impurity region.

According to the configuration of Item 28, the fourth impurity regionwith relatively high concentration of impurity is expanded toward thefirst impurity region, so charges generated at the p-n junction of thefirst impurity region and the periphery thereof move to the fourthimpurity region more readily. As a result, fewer minority carriers movefrom the first impurity region toward the charge accumulation region,and leak current is suppressed.

Item 29

The imaging device according to either Item 27 or 28, wherein the fourthimpurity region is not located directly beneath the other of the sourceand drain of the second transistor.

According to the configuration of Item 29, charges generated at the p-njunction of the other of the source and drain of the second transistorand the periphery thereof move to the fourth impurity region morereadily, due to the same reason as the configuration in Item 28. As aresult of fewer minority carriers moving from the first impurity regiontoward the charge accumulation region, leak current is suppressed.

Item 30

The imaging device according to any one of Items 25 through 29, furtherincluding:

a voltage supply circuit that applies a predetermined voltage to thethird impurity region, in at least a period in which signal chargesgenerated by the photoelectric converter are accumulated in the chargeaccumulation region more efficiently.

According to the configuration of Item 30, external voltage can beapplied to the third impurity region, so excess charges moving towardthe charge accumulation region can be recovered by the third impurityregion.

Item 31

The imaging device according to Item 30, wherein a voltage common withthe voltage applied to the third impurity region is applied to thesecond impurity region in the charge accumulation period.

According to the configuration of Item 31, the potential of the secondimpurity region and the third impurity region is fixed in the chargeaccumulation period, so contamination of the charge accumulation regionby minority carriers can be suppressed even more effectively.

Embodiments of the present disclosure will be described in detail below,with reference to the drawings. Note that the embodiments describedbelow are all general or specific examples of the technology of thepresent disclosure. Accordingly, values, shapes, materials, components,layout and connection state of the components, steps, the order ofsteps, and so forth illustrated in the following embodiments, are onlyexemplary, and are not intended to restrict the present disclosure.Various aspects described in the present embodiment may be combined witheach other to the extent that there is no conflict. Components in thefollowing embodiments which are not included in an independent Claimindicating a highest order concept are described as optional components.Components having substantially the same functions may be denoted bycommon reference numerals, and description thereof omitted in thedescription below. Also, illustration of a part of the elements may beomitted, to avoid the drawings from becoming excessively complicated.

First Embodiment

FIG. 1 illustrates an exemplary configuration of an imaging deviceaccording to a first embodiment of the present disclosure. The imagingdevice 100A illustrated in FIG. 1 has multiple pixels 10 formed on asemiconductor substrate 60, and peripheral circuits.

The pixels 10 each include a photoelectric converter 12. Thephotoelectric converter 12 receives incident light, and generatespositive and negative charges, typically a hole-electron pair. Thephotoelectric converter 12 may be a photoelectric conversion structureincluding a photoelectric conversion layer disposed above thesemiconductor substrate 60, and may be a photodiode formed on thesemiconductor substrate 60. Although the photoelectric converters 12 ofthe pixels 10 are illustrated in FIG. 1 as being spatially separatedfrom each other, but this is only for convenience in describing, and thephotoelectric converters 12 of the multiple pixel 10 may be continuouslylaid out on the semiconductor substrate 60 without spacing therebetween.

In the example illustrated in FIG. 1, the pixels 10 are arrayed inmultiple rows and columns, of m rows and n columns. Here, m and n areindependent integers of 1 or greater. A two-dimensional array, forexample, of the pixels 10 on the semiconductor substrate 60, forms animaging region R1. In a case where pixels 10 have a photoelectricconversion structure above the semiconductor substrate 60, for example,as the photoelectric converters 12, the imaging region R1 can be definedas a region of the semiconductor substrate 60 that is covered by thephotoelectric conversion structure.

The number and layout of the pixels 10 is not restricted to thoseillustrated. For example, the number of pixels 10 included in theimaging device 100A may be one. Although the pixels 10 are arrayed withthe centers thereof located on grid points of a square grid in thisexample, the multiple pixels 10 may be laid out such that the centers ofthe pixels 10 are located on grid points of a triangular grid, ahexagonal grid, or the like, for example. The imaging device 100A may beused as a line sensor by arraying the pixels 10 one-dimensionally, forexample.

The peripheral circuits in the configuration exemplified in FIG. 1include a vertical scanning circuit 42 and a horizontal signal readoutcircuit 44. The peripheral circuits may additionally include a controlcircuit 46, as exemplified in FIG. 1. The peripheral circuits mayfurther include a voltage supply circuit that supplies a predeterminedvoltage to the pixels 10 and so forth, for example, which will bedescribed later. The peripheral circuits may further include a signalprocessing circuit, output circuit, and so forth.

The vertical scanning circuit 42 is also referred to as a row scanningcircuit, and connects to address signal lines 34 provided correspondingto each row of the multiple pixels 10. The signal line providedcorresponding to each row of the multiple pixels 10 is not restricted tothe address signal line 34, and multiple types of signal lines may beconnected to the vertical scanning circuit 42 for each row of multiplepixels 10, which will be described later. The horizontal signal readoutcircuit 44 is also referred to as a column scanning circuit, and hasconnections with vertical signal lines 35 provided corresponding to eachcolumn of the multiple pixels 10.

The control circuit 46 receives command data, clock, and so forth,provided from the outside of the imaging device 100A for example, andcontrols the entire imaging device 100A. Typically, the control circuit46 has a timing generator, and supplies drive signals to the verticalscanning circuit 42, horizontal signal readout circuit 44,later-described voltage supply circuit, and so forth. Note that thearrows extending from the control circuit 46 in FIG. 1 schematicallyrepresent the flow of output signals from the control circuit 46. Thecontrol circuit 46 may be realized by a microcontroller including one ormore processor, for example. The functions of the control circuit 46 maybe realized by a combination of general-purpose processing circuit andsoftware, or may be realized by hardware specialized for suchprocessing.

These circuits making up the peripheral circuits typically are laid outin a peripheral region R2 outside of the imaging region R1, asschematically illustrated in FIG. 1. The circuits included in theperipheral circuits are provided on the semiconductor substrate 60 inthe example illustrated in FIG. 1. Note however, that part of theperipheral circuits may be provided on another substrate that isdifferent from the semiconductor substrate 60 on which the pixels 10 areformed.

FIG. 2 schematically illustrates an exemplary circuit configuration ofthe imaging device according to the first embodiment of the presentdisclosure. Four pixels 10A, in a 2-row 2-column array, arerepresentatively illustrated in FIG. 2, to avoid the drawing frombecoming complicated. These pixels 10A each are an example of the pixels10 illustrated in FIG. 1. The pixels 10A each have a photoelectricconversion structure 12A serving as the photoelectric converter 12, andinclude a signal detection circuit 14A electrically connected to thephotoelectric conversion structure 12A. The photoelectric conversionstructure 12A includes a photoelectric conversion layer disposed abovethe semiconductor substrate 60, which will be described later in detailwith reference to the drawings. That is to say, a stacked imaging deviceis exemplified here as the imaging device 100A. Note that in the presentspecification, terms such as “above”, “below”, “upper face”, and “lowerface”, are used only to specify the relative positions among parts, anddo not restrict the attitude of the imaging device when in use.

The photoelectric conversion structures 12A of the pixels 10A haveconnection with an accumulation control line 31. When the imaging device100A is operating, a predetermined voltage is applied to theaccumulation control line 31. For example, in a case of using, of thepositive and negative charges generated by photoelectric conversion, thepositive charge as the signal charge, a positive voltage of around 10 V,for example, may be applied to the accumulation control line 31 when theimaging device 100A is operating. A case of using holes as signalcharges will be exemplified below.

In the configuration exemplified in FIG. 2, the signal detection circuit14A includes a signal detecting transistor 22, an address transistor 24,and a reset transistor 26. The signal detecting transistor 22, addresstransistor 24, and reset transistor 26 typically are field-effecttransistors formed on the semiconductor substrate 60 supporting thephotoelectric conversion structure 12A, which will be described later indetail with reference to the drawings. An example of using an N-channelmetal-oxide semiconductor (MOS) device as the transistors will bedescribed below, unless specifically stated otherwise.

The gate of the signal detecting transistor 22 is electrically connectedto the photoelectric conversion structure 12A, as schematicallyillustrated in FIG. 2. In the example illustrated here, a chargeaccumulation node FD connecting the gate of the signal detectingtransistor 22 to the photoelectric conversion structure 12A has afunction of temporarily storing charges generated by the photoelectricconversion structure 12A. Applying a predetermined voltage to theaccumulation control line 31 when operating enables holes, for example,to be accumulated at the charge accumulation node FD as a signal charge.The charge accumulation node FD includes an impurity region formed inthe semiconductor substrate 60 as a part thereof, which will bedescribed later with reference to the drawings.

The drain of the signal detecting transistor 22 is connected to powersource wiring 32 that supplies power source voltage VDD around 3.3 V forexample, to the pixels 10A when the imaging device 100A is operating.The source of the signal detecting transistor 22 is connected to thevertical signal line 35 via the address transistor 24. The signaldetecting transistor 22 receives supply of the power source voltage VDDat the drain thereof, and thereby outputs signal voltage in accordancewith the amount of the signal charge accumulated at the chargeaccumulation node FD.

The address signal line 34 is connected to the gate of the addresstransistor 24 connected between the signal detecting transistor 22 andthe vertical signal line 35. Accordingly, the vertical scanning circuit42 can read output of the signal detecting transistor 22 of a selectedpixel 10A to the corresponding vertical signal line 35 by applying, tothe address signal line 34, a row-selection signal that controls on andoff of the address transistor 24. Note that the layout of the addresstransistor 24 is not restricted to the example illustrated in FIG. 2,and may be between the drain of the signal detecting transistor 22 andthe power source wiring 32.

A load circuit 45 and column signal processing circuit 47 are connectedto each vertical signal line 35. The load circuit 45 makes up a sourcefollower circuit along with the signal detecting transistor 22. Thecolumn signal processing circuit 47 is also referred to as a row signalaccumulating circuit, and performs noise suppression signal processingof which correlated double sampling is representative, analog/digitalconversion, and so forth. The horizontal signal readout circuit 44sequentially reads signals from multiple column signal processingcircuits 47 to a horizontal common signal line 49. The load circuit 45and column signal processing circuit 47 may be a part of theabove-described peripheral circuits.

A reset signal line 36 that has a connection to the vertical scanningcircuit 42 is connected to the gate of the reset transistor 26. A resetsignal line 36 is provided to each row of multiple pixel 10A in the sameway as the address signal line 34. The vertical scanning circuit 42 canselect pixels 10A to be the object of resetting, in increments of rows,by applying row selection signals to the address signal line 34. Thevertical scanning circuit 42 can switch the reset transistors 26 of theselected row on and off by applying a reset signal to the gate of thereset transistor 26 via the reset signal line 36. The potential of thecharge accumulation node FD is reset by the reset transistor 26 goingon.

In this example, one of the drain and source of the reset transistor 26is connected to the charge accumulation node FD, and the other of thedrain and source is connected to a corresponding one of feedback lines53 provided to each row of the multiple pixels 10A. That is to say, thevoltage of the feedback line 53 is supplied to the charge accumulationnode FD as reset voltage to initialize the charge of the photoelectricconversion structure 12A in this example.

In the configuration exemplified in FIG. 2, the imaging device 100A hasa feedback circuit 16A that includes an inverting amplifier 50 in a partof its feedback path. An inverting amplifier 50 is provided to eachcolumn of the multiple pixels 10A, with the above-described feedbackline 53 being connected to the output terminal of a corresponding one ofthe multiple inverting amplifiers 50, as illustrated in FIG. 2. Theinverting amplifier 50 may be part of the above-described peripheralcircuits.

An inverting input terminal of the inverting amplifier 50 is connectedto the vertical signal line 35 of a corresponding column, as illustratedin FIG. 2. When the imaging device 100A is operating, reference voltageVref that is positive voltage of 1 V or around 1 V, for example, issupplied to the non-inverting input terminal of the inverting amplifier50. Turning the address transistor 24 and reset transistor 26 on enablesa feedback path for negative feedback of the pixel 10A to be formed, andformation of the feedback path causes the voltage of the vertical signalline 35 to converge to the input reference voltage Vref to thenon-inverting input terminal of the inverting amplifier 50. In otherwords, formation of the feedback path resets the voltage of the chargeaccumulation node FD, so that the voltage of the vertical signal line 35is Vref. The voltage of an optional magnitude within the range of powersource voltage to ground voltage can be used as the reference voltageVref. Forming the feedback path enables reset noise generated by thereset transistor 26 going off to be reduced. Details of suppression ofreset noise using feedback is described in International Publication No.2012/147302. International Publication No. 2012/147302 is incorporatedherein by reference in its entirely, for reference.

Device Structure of Pixel 10A

FIG. 3A schematically illustrates an example of the device structure ofthe pixel 10A. The pixel 10A includes a semiconductor substrate 60A, thephotoelectric conversion structure 12A disposed above the semiconductorsubstrate 60A, and a conductive structure 89. The photoelectricconversion structure 12A is supported by an inter-layer insulating layer90 that covers the semiconductor substrate 60A, and the conductivestructure 89 is disposed in the inter-layer insulating layer 90, asillustrated in FIG. 3A. In the exemplified example, the inter-layerinsulating layer 90 includes multiple insulating layers, and theconductive structure 89 includes part of each of multiple wiring layersdisposed in the inter-layer insulating layer 90. The multiple wiringlayers disposed in the inter-layer insulating layer 90 may include awiring layer that includes the address signal line 34 and reset signalline 36 and so forth as a part thereof, a wiring layer that includes thevertical signal line 35, power source wiring 32, and feedback line 53and so forth as a part thereof, and so forth. It is needless to say thatthe number of insulating layers and number of wiring layers in theinter-layer insulating layer 90 is not restricted to this example, andis optionally settable.

The photoelectric conversion structure 12A includes a pixel electrode 12a formed on the inter-layer insulating layer 90, an opposing electrode12 c on the incident light side, and a photoelectric conversion layer 12b disposed between these electrodes. The photoelectric conversion layer12 b of the photoelectric conversion structure 12A is formed of anorganic material or an inorganic material such as amorphous silicon orthe like, and generates positive and negative charges by photoelectricconversion upon receiving incident light via the opposing electrode 12c. The photoelectric conversion layer 12 b typically is formedcontinuously over multiple pixels 10A. The photoelectric conversionlayer 12 b may include a layer made up of an organic material and alayer made up of an inorganic material.

The opposing electrode 12 c is a translucent electrode formed of atransparent conductive material such as indium tin oxide (ITO) or thelike. Note that the term “translucent” as used in the presentspecification means that at least part of light of a wavelength that thephotoelectric conversion layer 12 b can absorb is transmitted, andtransmission of light over the entire wavelength spectrum of visiblelight is not indispensable. Typically, the opposing electrode 12 c isformed over multiple pixels 10A in the same way as the photoelectricconversion layer 12 b. The opposing electrode 12 c has a connection withthe above-described accumulation control line 31, although this isomitted from illustration in FIG. 3A. When the imaging device 100A isoperating, the potential of the accumulation control line 31 iscontrolled so that the potential of the opposing electrode 12 c ishigher, for example, than the potential of the pixel electrode 12 a.Accordingly, positive charge of the positive and negative chargesgenerated by the photoelectric conversion can be selectively collectedby the pixel electrode 12 a. The opposing electrode 12 c may be formedas a single continuous layer over multiple pixels 10A. Accordingly, apredetermined potential can be applied in a batch to the opposingelectrode 12 c of the multiple pixels 10A.

The pixel electrode 12 a is an electrode formed of metal such asaluminum, copper, or the like, a metal nitride, or polysilicon that hasbeen imparted conductivity by being doped by an impurity, or the like.The pixel electrode 12 a is electrically isolated from the pixelelectrodes 12 a of other pixels 10A by being spatially isolated from thepixel electrodes 12 a of adjacent other pixels 10A.

The conductive structure 89 typically includes multiple lines and plugsformed of metal such as copper, tungsten, or the like, or metalcompounds such as metal nitrides or metal oxides, and polysilicon plugs.One end of the conductive structure 89 is connected to the pixelelectrode 12 a. The pixel electrode 12 a of the photoelectric conversionstructure 12A and the circuits on the semiconductor substrate 60A areelectrically connected to each other, by the other end of the conductivestructure 89 being connected to circuit elements formed on thesemiconductor substrate 60A, which will be described later.

Giving attention to the semiconductor substrate 60A now, thesemiconductor substrate 60A includes a supporting substrate 61, and oneor more semiconductor layers formed on the supporting substrate 61, asschematically illustrated in FIG. 3A. A p-type silicon substrate isexemplified here as the supporting substrate 61.

In the configuration exemplified illustrated in FIG. 3A, thesemiconductor substrate 60A has a p-type semiconductor layer 61 p on thesupporting substrate 61, an n-type semiconductor layer 62 n on thep-type semiconductor layer 61 p, a p-type semiconductor layer 63 p onthe n-type semiconductor layer 62 n, and a p-type semiconductor layer 65p located on the p-type semiconductor layer 63 p. In this example, thep-type semiconductor layer 63 p is formed generally over the entire faceof the supporting substrate 61. The p-type semiconductor layer 65 p thatserves as a first semiconductor layer, the n-type semiconductor layer 62n that serves as a second semiconductor layer, the p-type semiconductorlayer 63 p that serves as a third semiconductor layer, and the p-typesemiconductor layer 61 p, are each typically formed by ion injection ofan impurity to a semiconductor layer formed by epitaxial growth.

The concentration of the impurity at the p-type semiconductor layer 63 pand the p-type semiconductor layer 65 p is higher than the concentrationof the impurity at the p-type semiconductor layer 61 p. Theconcentration of the impurity at the p-type semiconductor layer 63 p ishigher than that of the p-type semiconductor layer 65 p here. Theconcentration of the impurity at the p-type semiconductor layer 61 p isaround 10¹⁵ cm⁻³ for example, and concentration of the impurity at thep-type semiconductor layer 65 p is around 10¹⁷ cm⁻³ for example. Theconcentration of the impurity at the p-type semiconductor layer 63 p maybe around 10¹⁸ cm⁻³ for example. Note that the mutual relation of theconcentrations of impurities above is only one example, and aconfiguration may be employed where the concentrations of impurities inthe p-type semiconductor layer 63 p and the p-type semiconductor layer65 p are around the same as each other. Alternatively, the concentrationof the impurity at the p-type semiconductor layer 65 p may be higherthan the concentration of the impurity at the p-type semiconductor layer63 p.

The n-type semiconductor layer 62 n is located between the p-typesemiconductor layer 61 p and p-type semiconductor layer 63 p. An unshownwell contact is connected to the n-type semiconductor layer 62 n,although omitted from illustration in FIG. 3A. The well contact isprovided on the outer side of the imaging region R1, and the potentialof the n-type semiconductor layer 62 n is controlled via the wellcontact when the imaging device 100A is operating. Providing the n-typesemiconductor layer 62 n suppresses inflow of minority carriers to thecharge accumulation region where signal charges are accumulated from thesupporting substrate 61 or peripheral circuits.

Further, in this example, the semiconductor substrate 60A has a p-typeregion 64 provided between the p-type semiconductor layer 63 p andp-type supporting substrate 61, penetrating the p-type semiconductorlayer 61 p and n-type semiconductor layer 62 n. The p-type region 64 hasa higher concentration of impurity as compared to the p-typesemiconductor layer 63 p and p-type semiconductor layer 65 p, and has afunction of electrically connecting the p-type semiconductor layer 63 pand supporting substrate 61 to each other.

The supporting substrate 61 has connection with a substrate contactomitted from illustration in FIG. 3A, provided on the outer side of theimaging region R1. When the imaging device 100A is operating, thepotential of the supporting substrate 61 and p-type semiconductor layer63 p is controlled via the substrate contact. The potential of thep-type semiconductor layer 65 p can also be controlled via the p-typesemiconductor layer 63 p when the imaging device 100A is operating, dueto the p-type semiconductor layer 65 p being located so as to be incontact with the p-type semiconductor layer 63 p. Voltage of 0 V, forexample, may be applied to the p-type semiconductor layer 65 p via thesubstrate contact when the imaging device 100A is operating.

In the configuration exemplified in FIG. 3A, the p-type semiconductorlayer 65 p has a p-type impurity region 66 p having a lowerconcentration of impurity as a part of the p-type semiconductor layer 65p, and an n-type impurity region 67 n is formed in the p-type impurityregion 66 p. The n-type impurity region 67 n is formed near the surfaceof the semiconductor substrate 60A, with at least part thereof beinglocated on the surface of the semiconductor substrate 60A. The n-typeimpurity region 67 n here includes a first region 67 a, and a secondregion 67 b that is located within the first region 67 a and has arelatively higher concentration of impurity than the first region 67 a.The concentration of impurity of the first region 67 a is around 10¹⁷cm⁻³ for example, and the concentration of impurity of the second region67 b is around 3×10¹⁸ cm⁻³ for example.

An insulating layer is disposed on the principal face of thesemiconductor substrate 60A, on the side toward the photoelectricconversion structure 12A. In this example, the principal face of thesemiconductor substrate 60A on the side toward the photoelectricconversion structure 12A is covered by a first insulating layer 71, asecond insulating layer 72, and a third insulating layer 73. The firstinsulating layer 71 is a thermally oxidized film of silicon, forexample. The second insulating layer 72 is a silicon dioxide layer forexample, and the third insulating layer 73 is a silicon nitride layer,for example. The second insulating layer 72 may have a layered structureincluding multiple insulating layers, and in the same way, the thirdinsulating layer 73 may have a layered structure including multipleinsulating layers.

The layered structure of the first insulating layer 71, secondinsulating layer 72, and third insulating layer 73 has a contact hole h1on the second region 67 b of the n-type impurity region 67 n. A contactplug Cp1 that is part of the conductive structure 89 is connected to thesecond region 67 b via the contact hole h1 in the example illustrated inFIG. 3A. Accordingly, the n-type impurity region 67 n is electricallyconnected to the pixel electrode 12 a of the photoelectric conversionstructure 12A via the conductive structure 89.

The junction capacitance formed by the p-n junction between the p-typeimpurity region 66 p serving as a p-well and the n-type impurity region67 n functions as capacitance that accumulates at least part of thesignal charges. That is to say, the n-type impurity region 67 nfunctions as a charge accumulation region temporarily storing signalcharges. The conductive structure 89 and n-type impurity region 67 n canalso be said to make up at least part of the above-described chargeaccumulation node FD.

The potential of the p-type semiconductor layer 65 p can be controlledvia the p-type semiconductor layer 63 p when the imaging device 100A isoperating, by placing the p-type semiconductor layer 65 p adjacent tothe p-type semiconductor layer 63 p, as described above. Employing thissort of structure enables a region with relatively low concentration ofimpurity to be disposed in the periphery of the portion where thecontact plug Cp1, which has electrical contact with the photoelectricconversion structure 12A, and the semiconductor substrate 60A come intocontact. That is to say, the first region 67 a and p-type impurityregion 66 p can be disposed around the second region 67 b of the n-typeimpurity region 67 n as in this example. Disposing the first region 67 athat has a relatively low concentration of impurity around the secondregion 67 b enables the intensity of the electrical field formed by thep-n junction between the n-type impurity region 67 n and p-type impurityregion 66 p to be reduced. Reducing the intensity of the electricalfield formed by the p-n junction yields an effect of suppressing leakcurrent due to the electrical field formed by the p-n junction.

Note that forming the second region 67 b in the n-type impurity region67 n is not indispensable. Note however, that making the concentrationof impurity of the second region 67 b that is the contact portion withthe contact plug Cp1 and semiconductor substrate 60A relatively highyields the effect of suppressing spread of the depletion layer aroundthe portion where the contact plug Cp1 and semiconductor substrate 60Acome into contact. This also enables suppression of crystal defects inthe semiconductor substrate 60A at the interface of the contact plug Cp1and semiconductor substrate 60A, in other words, unintended inflow ofcharges to the n-type impurity region 67 n serving as the chargeaccumulation region and/or unintended outflow of charges from the n-typeimpurity region 67 n, occurring due to the interface state. Also,connecting the contact plug Cp1 to the second region 67 b that has arelatively high concentration of impurity yields the effect of reducedcontact resistance.

The above-described signal detection circuit 14A is formed on thesemiconductor substrate 60A. The signal detection circuit 14A in thepixel 10A is electrically isolated from the signal detection circuits14A in other adjacent pixels 10A due to a pixel isolation region 69being disposed between mutually adjacent pixels 10A. The pixel isolationregion 69 is, for example, a p-type diffusion region.

In the signal detection circuit 14A, the reset transistor 26 includesthe n-type impurity region 67 n as one of the drain region and sourceregion, and includes an n-type impurity region 68 an as the other of thedrain region and source region. The reset transistor 26 further includesa gate electrode 26 e on the first insulating layer 71, with the portionof the first insulating layer 71 located between the gate electrode 26 eand the semiconductor substrate 60A functioning as a gate insulatinglayer of the reset transistor 26. The n-type impurity region 68 an isformed in the p-type semiconductor layer 65 p, and is connected to afeedback line 53 via a contact hole h2.

Also, n-type impurity regions 68 bn, 68 cn, and 68 dn are provided inthe p-type semiconductor layer 65 p. The n-type impurity regions 68 an,68 bn, 68 cn, and 68 dn have a higher concentration of impurity than thefirst region 67 a of the n-type impurity region 67 n.

The signal detecting transistor 22 includes the n-type impurity region68 bn, the n-type impurity region 68 cn, and a gate electrode 22 e onthe first insulating layer 71. The gate electrode 22 e in this exampleis connected to a portion of the conductive structure 89 where the pixelelectrode 12 a and contact plug Cp1 come into contact, in the layerwhere the address signal line 34, reset signal line 36, and so forth arelocated, as schematically illustrated by the dashed line in FIG. 3A. Inother words, the conductive structure 89 also has electrical connectionwith the gate electrode 22 e.

The n-type impurity region 68 bn serving as a drain region is connectedto a contact plug Cp3 via a contact hole h3. The above-described powersource wiring 32 serving as the source follower power source isconnected to the contact plug Cp3. Note that the power source wiring 32is omitted from illustration in FIG. 3A.

The n-type impurity region 68 bn is located in the p-type semiconductorlayer 65 p, isolated from the n-type impurity region 67 n serving as thecharge accumulation region, as schematically illustrated in FIG. 3A. Inthis example, an impurity region 69 n and p-type impurity regions 69 paand 69 pb are interposed between the n-type impurity region 68 bn andn-type impurity region 67 n, thereby electrically isolating the n-typeimpurity region 68 bn from the n-type impurity region 67 n. Also, thep-type impurity region 66 p extends to the position of the n-typeimpurity region 68 bn, and the above-described impurity region 69 n andp-type impurity regions 69 pa and 69 pb are disposed in the p-typeimpurity region 66 p that has a relatively low impurity concentration inthe p-type semiconductor layer 65 p in this example. When viewing across-sectional taken perpendicular to the principal face of thesemiconductor substrate 60A, the impurity regions 69 pa and 69 pb aredisposed in the p-type impurity region 66 p isolated from each other,between the n-type impurity region 68 bn and the n-type impurity region67 n, as schematically illustrated in FIG. 3A. The impurity regions 69pa and 69 pb are each part of the above described pixel isolation region69, and typically are p-type diffusion regions. The concentration ofimpurity in the impurity regions 69 pa and 69 pb is in a range around10¹⁸ cm⁻³ or more to 5×10¹⁸ cm⁻³ or less, for example.

The n-type impurity region 69 n having a different conductivity type islocated between the p-type impurity regions 69 pa and 69 pb. Theimpurity region 69 n is typically an n-type diffusion region. Theimpurity region 69 n has around the same impurity concentration as thefirst region 67 a of the n-type impurity region 67 n or higher. That isto say, the impurity region 69 n may have a concentration of impurityaround 10¹⁷ cm⁻³ or more, for example. Providing the n-type impurityregion 69 n and p-type impurity regions 69 pa and 69 pb between then-type impurity region 68 bn and n-type impurity region 67 n enablescharges that are generated at the p-n junction of the n-type impurityregion 68 bn and move toward the n-type impurity region 67 n to be movedto the impurity region 69 n by potential gradient, which will bedescribed later with reference to the drawings.

At least part of the impurity region 69 n is located on the surface ofthe semiconductor substrate 60A, as schematically illustrated in FIG.3A. In the same way, at least part of the impurity region 69 pa and atleast part of the impurity region 69 pb are also located on the surfaceof the semiconductor substrate 60A. Accordingly, the impurity region 69pa, the impurity region 69 n, and the impurity region 69 pb aredisposed, in this order, in the direction heading from the impurityregion 69 pa toward the impurity region 69 pb on the surface of thep-type semiconductor layer 65 p. The impurity region 69 pa and impurityregion 69 pb may be located so as to surround the impurity region 69 nin plan view. In other words, no p-type region with a relatively highconcentration is disposed at least below the impurity region 69 n.Employing such a layout enables occurrence of leak current due to a p-njunction being formed between the p-type impurity region and n-typeimpurity region 69 n to be avoided, as compared to a configuration wherethe n-type impurity region 69 n is provided in a high-concentrationp-type impurity region.

Note that in the configuration exemplified in FIG. 3A, part of thep-type impurity region 66 p is further interposed between the impurityregion 69 pa and impurity region 69 pb, and between the impurity region69 pb and impurity region 69 n. Placing the impurity region 69 pa andimpurity region 69 pb in the p-type impurity region 66 p with a spacingfrom the impurity region 69 n in this way enables formation of a p-njunction due to a relatively high-concentration p-type region and arelatively high-concentration n-type region coming into contact to beavoided, and occurrence of leak current can be further suppressed.

As described above, relatively high voltage of around 3.3 V is appliedto the n-type impurity region 68 bn functioning as a drain region of thesignal detecting transistor 22 when the imaging device 100A isoperating. According to studies made by the present inventors, whenelectrons are generated at a p-n junction formed between a drain regionwhere high voltage is applied and the perimeter thereof, part of theelectrons can flow into the charge accumulation region due to diffusionthrough the interface state of the element isolation region and theinterface state of the surface of the silicon substrate. This sort ofleak current that occurs due to excess charge flowing into the chargeaccumulation region can become a cause of deterioration in the obtainedimage.

However according to the first embodiment of the present disclosure, theimpurity regions 69 pa, 69 pb, and 69 n are interposed between then-type impurity region 68 bn and the n-type impurity region 67 n servingas the charge accumulation region. Accordingly, charges generated at thep-n junction of the n-type impurity region 68 bn and moving by diffusiontoward the n-type impurity region 67 n can be collected at the impurityregion 69 n before reaching the n-type impurity region 67 n. That is tosay, even in a case where there is occurrence of charges generated atthe p-n junction of the n-type impurity region 68 bn and moving towardthe n-type impurity region 67 n, contamination by excess charges to then-type impurity region 67 n that accumulates signal charges can besuppressed, and image deterioration due to leak current can besuppressed.

From this perspective, the impurity regions 69 pa, 69 pb, and 69 n canbe collectively referred to as a leak current blocking structure. Forthe sake of convenience, the structure including the impurity regions 69pa, 69 pb, and 69 n may be collectively referred to as “blockingstructure 28A” hereinafter. Providing the blocking structure 28A in thepixel blocks movement of minority carriers to the n-type impurity region67 n by the blocking structure 28A, and as a result, the effects ofsuppressed leak current from contamination of the n-type impurity region67 n by minority carriers can be obtained.

The address transistor 24 is further formed on the semiconductorsubstrate 60A. The address transistor 24 includes the n-type impurityregion 68 cn, an n-type impurity region 68 dn and a gate electrode 24 eon the first insulating layer 71. The n-type impurity region 68 cnfunctions as a drain region of the address transistor 24, and the n-typeimpurity region 68 dn functions as a source region of the addresstransistor 24. The portion of the first insulating layer 71 that islocated between the gate electrode 24 e and the semiconductor substrate60A functions as a gate insulating film of the address transistor 24. Inthis example, the n-type impurity region 68 cn is shared between theaddress transistor 24 and the signal detecting transistor 22, so thesetransistors are electrically connected to each other. The verticalsignal line 35 is connected to the n-type impurity region 68 dn via acontact hole h4, as schematically illustrated in FIG. 3A.

First Modification

FIG. 3B schematically illustrates an exemplary configuration of theimaging device according to a first modification of the firstembodiment. The primary difference between the pixel As illustrated inFIG. 3B and the pixel 10A described with reference to FIG. 3A is that inthe pixel As, a p-type semiconductor layer 63 ps is provided in thesemiconductor substrate 60A instead of the p-type semiconductor layer 63p.

The p-type semiconductor layer 63 ps is formed in a region other thandirectly below the impurity region 69 n on the n-type semiconductorlayer 62 n, as schematically illustrated in FIG. 3B. In other words, thep-type semiconductor layer 63 ps has an opening at the portion directlybelow the impurity region 69 n. The impurity region 69 pa that is partof the p-type impurity region 66 p is located inside this opening, asillustrated in FIG. 3B.

As described above, the concentration of impurity of the p-type impurityregion 66 p is lower in comparison with the p-type semiconductor layer65 p. Accordingly, the p-type impurity region 69 pa has a lowerconcentration of impurity than the p-type semiconductor layer 63 p. Theconcentration of impurity in the p-type impurity region 69 pa may bearound 10¹⁶ cm⁻³ for example. Providing a region with relatively lowconcentration of impurity to part of the p-type semiconductor layer 63p, and particularly at the position directly below the impurity region69 n, can cause the n-type semiconductor layer 62 n to absorb unwantedminority carriers moving toward the n-type impurity region 67 n, whichwill be described later by way of examples. As a result, the inflow ofunwanted current to the n-type impurity region 67 n serving as a chargeaccumulation region is suppressed even further, and effects ofsuppressed leak current can be anticipated.

Second Modification

FIG. 4 schematically illustrates an exemplary configuration of theimaging device according to the second modification of the firstembodiment. The imaging device 100B illustrated in FIG. 4 further has avoltage supply circuit 48 disposed in the peripheral region R2 ascompared with the imaging device 100A illustrated in FIG. 1.

The voltage supply circuit 48 supplies a predetermined voltage to thepixels 10 via a voltage line 38, based on drive signals from the controlcircuit 46, as schematically illustrated in FIG. 4. The voltage supplycircuit 48 is not restricted to a particular power source circuit, andmay be a circuit that converts voltage supplied from a power source suchas a battery to a predetermined voltage, or may be a circuit thatgenerates a predetermined voltage. The voltage supply circuit 48 may bepart of the above-described vertical scanning circuit 42.

FIG. 5 schematically illustrates the device structure of a pixel thatthe imaging device 100 b illustrated in FIG. 4 has. The gate electrode22 e is electrically connected to the conductive structure 89 at thelayer where the address signal line 34, reset signal line 36, and soforth are located in the pixel 10B illustrated in FIG. 5 in the same wayas the examples illustrated in FIGS. 3A and 3B.

The pixel 10B illustrated in FIG. 5 has a blocking structure 28B insteadof the blocking structure 28A, in comparison with the pixel As describedwith reference to FIG. 3B. The blocking structure 28B further includes acontact plug Cp8, in addition to the impurity regions 69 pa and 69 pband the impurity region 69 n. The contact plug Cp8 is in contact withthe impurity region 69 n via a contact hole h8 provided to the firstinsulating layer 71, the second insulating layer 72, and the thirdinsulating layer 73. The contact plug Cp8 electrically connects theimpurity region 69 n and the voltage line 38 to each other, asschematically illustrated in FIG. 5. Although the voltage line 38 isillustrated as being in the same layer as the address signal line 34 andreset signal line 36 in FIG. 5, the voltage line 38 has no electricalconnection with any of the address signal line 34, reset signal line 36,and conductive structure 89.

The voltage line 38 has connection with the voltage supply circuit 48,as described with reference to FIG. 4. That is to say, the blockingstructure 28B is configured to be capable of applying voltage to theimpurity region 69 n via the voltage line 38 in this example. Whenoperating, the voltage supply circuit 48 supplies voltage to theimpurity region 69 n of the blocking structure 28 that is inverse biasas to the p-type semiconductor layer 65 p, for example. That is to say,the voltage supply circuit 48 supplies voltage that is higher than thatof the p-type semiconductor layer 65 p to the impurity region 69 n ofthe blocking structure 28B. Alternatively, the voltage supply circuit 48may apply voltage to the impurity region 69 n via the voltage line 38 sothat the impurity region 69 n and p-type semiconductor layer 65 p areequipotential when operating. An example of a voltage where the impurityregion 69 n and p-type semiconductor layer 65 p are equipotential may bevoltage of 0 V.

Application of voltage by the voltage supply circuit 48 does not have tobe perpetually executed when the imaging device 100B is operating, andit is sufficient to be executed in at least exposure periods, i.e., incharge accumulation periods where charge generated by the photoelectricconversion structure 12A is being accumulated in the n-type impurityregion 67 n. Applying voltage to the impurity region 69 n can enableexcess charges moving toward the n-type impurity region 67 n serving asthe charge accumulation region to be recovered by the impurity region 69n more efficiently. The voltage applied to the blocking structure 28Bmay be supplied from the vertical scanning circuit 42 instead.

As described above, the potential of the supporting substrate 61 and thep-type semiconductor layer 63 p is controlled via substrate contacts.That is to say, controlling voltage applied to substrate contacts cancontrol the potential of the p-type semiconductor layer 65 p disposed onthe p-type semiconductor layer 63 p, and further control the potentialof the impurity regions 69 pa and 69 pb disposed in the p-typesemiconductor layer 65 p. In other words, different voltages from eachother can be individually applied to the impurity region 69 n in theblocking structure 28B, and the impurity regions 69 pa and 69 pb in theblocking structure 28B.

FIG. 6A schematically illustrates an example of electrical connectionbetween the pixel 10B and voltage supply circuit 48. In theconfiguration exemplified in FIG. 6A, a second voltage supply circuit 48b is connected to a substrate contact 61C. The voltage supply circuit 48b can control the potential of the impurity regions 69 pa and 69 pb inthe blocking structure 28B via the supporting substrate 61, p-typeregion 64, p-type semiconductor layer 63 p, and p-type semiconductorlayer 65 p, by supplying voltage to the substrate contact 61C. Voltagethat is applied to the impurity regions 69 pa and 69 pb via thesubstrate contact 61C is lower than voltage applied to the impurityregion 69 n via the voltage line 38, for example. Alternatively, thesame voltage, e.g., voltage of 0 V may be applied to the impurityregions 69 pa and 69 pb via the substrate contact 61C so that theimpurity regions 69 pa and 69 pb, the p-type semiconductor layer 65 p,and the impurity region 69 n are equipotential. It is sufficient forapplication of voltage from outside of the impurity regions 69 pa and 69pb to be performed selectively at least in charge accumulation periods,in the same way as voltage application of the blocking structure 28B tothe impurity region 69 n. An arrangement may be made where twoindividual voltage supply circuits are not provided, and voltage isindependently supplied to the impurity region 69 n and the substratecontact 61C by a single voltage supply circuit.

FIG. 6B schematically illustrates another example of electricalconnection between the pixel 10B and the voltage supply circuit 48. Inthe example illustrated in FIG. 6A, the voltage line 38 is connected notonly to the impurity region 69 n, but also to the n-type semiconductorlayer 62 n, by being connected to a well contact 62C. That is to say, inthe configuration exemplified in FIG. 6B, the voltage supply circuit 48can apply common voltage to both the impurity region 69 n and n-typesemiconductor layer 62 n, in charge accumulation periods for example.The voltage applied to the n-type semiconductor layer 62 n via the wellcontact 62C may be a voltage where the impurity region 69 n has reversebias as to the p-type semiconductor layer 65 p. That is to say, thevoltage applied to the n-type semiconductor layer 62 n via the wellcontact 62C may be a higher voltage than that of the p-typesemiconductor layer 65 p. Alternatively, this may be a voltage where theimpurity region 69 n and p-type semiconductor layer 65 p becomeequipotential, such as voltage of 0 V, for example. Of course, thepotential of the impurity regions 69 pa and 69 pb in the blockingstructure 28B may be further controlled via the substrate contact 61C,as in the example described with reference to FIG. 6A.

For example, voltage may be applied to the n-type semiconductor layer 62n and impurity region 69 n that is reverse bias as to the p-typesemiconductor layer 65 p. That is to say, voltage that is higher thanthat of the p-type semiconductor layer 65 p may be applied to the n-typesemiconductor layer 62 n and impurity region 69 n. This sort of voltageapplication enables minority carriers that cause leak current to beabsorbed by the blocking structure 28B even more efficiently. That is tosay, applying voltage to both the impurity region 69 n and n-typesemiconductor layer 62 n enables excess changes moving toward the n-typeimpurity region 67 n serving as the charge accumulation region to berecovered by the impurity region 69 n or n-type semiconductor layer 62 neven more efficiently.

FIG. 7 schematically illustrates yet another example of electricalconnection to the blocking structure 28B. The voltage line 38 may beconnected to the n-type impurity region 68 an of the reset transistor 26instead of the feedback line 53, as illustrated in FIG. 7. That is tosay, the voltage supply circuit 48 also functions as a reset voltagesource to supply reset voltage to the pixels in this example. Supplyinga common voltage to the reset transistor 26 and the impurity region 69 nof the blocking structure 28B does away with the need to provide aseparate reset voltage source, which is advantageous with regard toreduction in size of the imaging device.

Third Modification

FIG. 8 illustrates a third modification of the imaging device accordingto the first embodiment. FIG. 8 illustrates an exemplary circuitconfiguration of a pixel 10C that has been representatively selectedfrom pixels 10C according to the third modification of the imagingdevice. A signal detection circuit 14C of the pixel 10C illustrated inFIG. 8 further includes, in addition to the signal detecting transistor22, address transistor 24, and reset transistor 26, a bandwidth controltransistor 56, a first capacitive element 51, and a second capacitiveelement 52, in comparison with the signal detection circuit 14Aillustrated in FIG. 2.

The bandwidth control transistor 56 is connected between the resettransistor 26 and feedback line 53, and the gate thereof is connected toa feedback control line 58. The feedback control line 58 is connected tothe vertical scanning circuit 42, for example, with the gate voltage ofthe bandwidth control transistor 56 being controlled by the verticalscanning circuit 42 when the imaging device is operating.

The first capacitive element 51 has a relatively small capacitancevalue, and is connected to the reset transistor 26 in parallel. Thesecond capacitive element 52 has a larger capacitance value than thefirst capacitive element 51, with one electrode being connected to anode RD between he reset transistor 26 and bandwidth control transistor56, and the other electrode of the second capacitive element 52 beingconnected to a sensitivity adjustment line 54. The sensitivityadjustment line 54 is connected to the vertical scanning circuit 42, forexample, and the potential thereof is set to 0 V, for example, when theimaging device 100 is operating.

A feedback path that includes the signal detecting transistor 22 and thebandwidth control transistor 56 in the path can be formed by turning thebandwidth control transistor 56 on. That is to say, the feedback pathformed by the feedback circuit 16C illustrated in FIG. 8 includes thebandwidth control transistor 56 in addition to the inverting amplifier50. The second capacitive element 52 and bandwidth control transistor 56may function as a resistor-capacitor (RC) filter circuit.

Formation of the feedback loop where part or all of the output signalsof the signal detecting transistor 22 are fed back electrically enablesthe effects of kTC noise that occurs when the reset transistor 26 andbandwidth control transistor 56 go off to be reduced. Details of suchnoise cancellation using feedback are described in Japanese UnexaminedPatent Application Publication No. 2017-046333. The reset transistor 26can also be made to function as a gain switching transistor in thecircuit configuration exemplified in FIG. 8. Details of such modeswitching are also described in Japanese Unexamined Patent ApplicationPublication No. 2017-046333. Japanese Unexamined Patent ApplicationPublication No. 2017-046333 is incorporated herein by reference in itsentirely, for reference.

The circuit configuration such as illustrated in FIG. 8, where thebandwidth control transistor 56 is connected between the resettransistor 26 and the feedback line 53, is advantageous from theperspective of noise reduction, since contamination by excess charges atthe node RD from the drain region of the signal detecting transistor 22,for example, can be suppressed, and leak current at the node RD can besuppressed. Applying a connection structure the same as that of thecharge accumulation node FD to the node RD enables leak current to besuppressed at the node RD, which will be described below.

Device Configuration of Pixel 10C

FIG. 9 schematically illustrates an example of the device structure ofthe pixel 10C illustrated in FIG. 8. In the configuration exemplified inFIG. 9, the pixel 10C includes a semiconductor substrate 76 thatsupports the photoelectric conversion structure 12A. The semiconductorsubstrate 76 has the supporting substrate 61, and multiple semiconductorlayers including the p-type semiconductor layer 63 ps on the supportingsubstrate 61, in the same way as the semiconductor substrate 60Aillustrated in FIGS. 3B and 5. The semiconductor substrate 76 has ap-type semiconductor layer 75 p formed on the p-type semiconductor layer63 ps. The concentration of impurity of the p-type semiconductor layer75 p may be around the same as that of the above-described p-typesemiconductor layer 65 p. The p-type semiconductor layer 75 p has thep-type impurity region 66 p and a p-type impurity region 76 p. Theconcentration of impurity of the p-type impurity region 76 p may bearound the same as that of the above-described p-type impurity region 66p. An n-type impurity region 77 n is formed on the p-type impurityregion 76 p. The n-type impurity region 77 n functions as one of thedrain region and source region of the reset transistor 26.

The n-type impurity region 77 n includes a first region 77 a, and asecond region 77 b located within the first region 77 a, in the same wayas the n-type impurity region 67 n. The first region 77 a has aconcentration of impurity that is around the same, for example, as thefirst region 67 a of the n-type impurity region 67 n. Alternatively, theconcentration of impurity of the first region 77 a is higher than thatof the first region 67 a of the n-type impurity region 67 n. This isbecause the tolerance value of leak current can be set higher for thenode RD as compared to the charge accumulation node FD. Parasiticresistance at the source side of the reset transistor 26, for example,can be reduced by making the concentration of impurity of the firstregion 77 a to be higher than the concentration of impurity of the firstregion 67 a, and the current driving performance of the reset transistor26 can be improved.

In the example exemplified in FIG. 9, the layered structure of the firstinsulating layer 71, second insulating layer 72, and third insulatinglayer 73 has a contact hole h5 provided in a region on the n-typeimpurity region 77 n. A contact plug Cp5 is connected to the n-typeimpurity region 77 n via this contact hole h5. The contact plug Cp5 isconnected to the second region 77 b of the n-type impurity region 77 nin this example. Now, the second region 77 b has a higher concentrationof impurity than the first region 77 a. Although formation of the secondregion 77 b having a high concentration of impurity within the n-typeimpurity region 77 n is not indispensable, forming the second region 77b within the n-type impurity region 77 n yields the effects of reducedcontact resistance.

The contact plug Cp5 is on the same layer as other contact plugs such asthe contact plug Cp1, and typically is formed by patterning of apolysilicon film. The contact plug Cp5 is connected to wiring 88 via ametal plug p5 disposed within the insulating layer 90 and so forth. Thewiring 88 is wiring connected to, out of the electrodes that the secondcapacitive element 52 has, the electrode at the side not connected tothe sensitivity adjustment line 54. In this example as well, the voltageline 38 is located in the same layer as the address signal line 34 andreset signal line 36, in the same way as the example described withreference to FIG. 5. However, the voltage line 38 is not electricallyconnected to any of the address signal line 34, reset signal line 36,and conductive structure 89. The first capacitive element 51 and secondcapacitive element 52 omitted from illustration in FIG. 9 may be formedin the pixel 10C in the form of a metal-insulator-semiconductor (MIS)structure, or may be formed in the form of a metal-insulator-meta (MIM)structure. Using the MIM structure enables a larger capacitance value tobe obtained.

The upper face of the contact plug Cp5 does not have a metal silicidelayer. Accordingly, the metal plug p5 is directly connected to the upperface of the contact plug Cp5 in this example. Directly connecting themetal plug p5 to the contact plug Cp5 without going through a metalsilicide layer enables dispersion of metal into the n-type impurityregion 77 n via the contact plug Cp5, particularly dispersion of nickel,to be prevented. In other words, contamination of the node RD by excesschanges can be suppressed, and noise at the pixel 10C can be furthersuppressed.

In the example exemplified in FIG. 9, the bandwidth control transistor56 shares the n-type impurity region 77 n with the reset transistor 26.That is to say, in the configuration exemplified in FIG. 9, the n-typeimpurity region 77 n also functions as one of the source region anddrain region of the bandwidth control transistor 56. The n-type impurityregion 68 an is formed in the p-type semiconductor layer 75 p in thesame way as the n-type impurity regions 68 bn through 68 dn, andfunctions as the other of the source region and drain region of thebandwidth control transistor 56.

The bandwidth control transistor 56 further has a gate electrode 56 elocated on the first insulating layer 71. The gate electrode 56 etypically is a polysilicon electrode, and is located in the same layeras the gate electrode 22 e of the signal detecting transistor 22, thegate electrode 24 e of the address transistor 24, and the gate electrode26 e of the reset transistor 26. The gate electrode of these transistorstypically is a polysilicon electrode that has been imparted conductivityby doping with an n-type impurity.

The pixel 10C also has the blocking structure 28B including the impurityregion 69 n interposed between the n-type impurity region 68 bn andn-type impurity region 67 n, in the same way as the example illustratedin FIG. 5. The blocking structure 28B further includes the contact plugCp8 connected to the impurity region 69 n, in comparison with theabove-described blocking structure 28A. The contact plug Cp8 isconnected to the impurity region 69 n via the contact hole h8 providedto the layered structure of the first insulating layer 71, secondinsulating layer 72, and third insulating layer 73, as schematicallyillustrated in FIG. 9. The contact plug Cp8 is also connected to thevoltage line 38, and is configured so that a predetermined voltage canbe applied from the voltage supply circuit 48.

FIG. 10 illustrates an example of the layout of elements in the pixel10C. Note that while the above-described FIG. 9 illustrates the signaldetecting transistor 22, address transistor 24, reset transistor 26, andbandwidth control transistor 56 all in the same cross-section, this isonly for the sake of convenience in describing. Accordingly, there maybe portions where the cross-section obtained by cutting the elementlayout illustrated in FIG. 10 along a certain line, and thecross-section illustrated in FIG. 9 do not coincide with each other.

In the configuration exemplified in FIG. 10, the reset transistor 26 andbandwidth control transistor 56 are arrayed on a straight line in thevertical direction of the plane of the drawing. Accordingly, the secondregion 77 b that is the connecting portion of the contact plug Cp5 andthe semiconductor substrate 76 is located between the gate electrode 26e of the reset transistor 26 and the gate electrode 56 e of thebandwidth control transistor 56. The signal detecting transistor 22 andaddress transistor 24 also are arrayed on a straight line in thevertical direction of the plane of the drawing. The vertical signal line35 also extends in the vertical direction of the plane of the drawing asshown in FIG. 10, and accordingly, the vertical direction of the planeof the drawing here is parallel to the column direction of the multiplepixels 10C.

The pixel isolation region 69 including the impurity regions 69 pa and69 pb in a part thereof is disposed at the periphery of regions wherethe set of reset transistor 26 and bandwidth control transistor 56, andthe signal detecting transistor 22 and the address transistor 24, havebeen formed. Accordingly, these regions are electrically isolated fromeach other by the pixel isolation region 69. In this example, theblocking structure 28B is located between the n-type impurity region 68bn and the n-type impurity region 67 n, and extends from one edgeportion of the pixel 10C to the other edge portion along the verticalsignal line 35 in plan view. The impurity region 69 n and the impurityregions 69 pa and 69 pb making up the blocking structure 28B alsoextends from one edge portion of the pixel 10C to the other edgeportion.

By positioning the blocking structure 28B between the n-type impurityregion 68 bn serving as the drain region of the signal detectingtransistor 22 and the n-type impurity region 67 n serving as the chargeaccumulation region, minority carriers generated at the n-type impurityregion 68 bn and moving toward the n-type impurity region 67 n can beblocked by the blocking structure 28B. Also, at least part of theblocking structure 28B is also located between the n-type impurityregion 68 bn and the n-type impurity region 77 n in this example, sominority carriers generated at the n-type impurity region 68 bn andmoving toward the n-type impurity region 77 n can be blocked by theblocking structure 28B. That is to say, occurrence of leak current atthe node RD can be suppressed as well. Particularly in this example, theimpurity regions 69 pa and 69 pb in the blocking structure 28B have alayout that sandwiches the impurity region 69 n, and the blockingstructure 28B extends from one edge portion of the pixel 10C to theother edge portion in plan view. Accordingly, effects of suppressingoccurrence of leak current due to movement of minority carriers from notonly the n-type impurity region 68 bn but also from the n-type impurityregions 68 cn and 68 dn toward the n-type impurity regions 67 n and 77 ncan be anticipated.

Further, a blocking structure 28Bb that extends over a region other thanthe region between the n-type impurity region 68 bn and the n-typeimpurity region 67 n or 77 n may be disposed in the pixel, asexemplified in FIG. 10. In the example exemplified in FIG. 10, theblocking structure 28Bb is disposed at the right side of the signaldetecting transistor 22 and address transistor 24 in the plane of thedrawing, extending form one edge portion of the pixel 10C to the otheredge portion along the vertical signal line 35. The blocking structure28Bb may have the same structure as the above-described blockingstructure 28B.

FIG. 11 illustrates an example of a two-dimensional array of the pixels10C illustrated in FIG. 10. The pixels 10C can be arrayedtwo-dimensionally on the semiconductor substrate 60A, for example, asdescribed earlier with reference to FIG. 1. It can be seen from FIG. 11that when the pixels 10C illustrated in FIG. 10 are two-dimensionallylaid out, the blocking structure 28Bb is located between, for example,the n-type impurity region 68 bn of the pixel 10C to which that blockingstructure 28Bb is provided, and the n-type impurity regions 67 n and 77n of the adjacent pixel 10C. That is to say, a blocking structure 28Bbalways is interposed between the n-type impurity region 68 dn and then-type impurity region 67 n that is closest to that n-type impurityregion 68 dn, in the row direction. Accordingly, inflow of excessminority carriers from the n-type impurity region 68 dn or the like of acertain pixel 10C to the n-type impurity region 67 n of a pixel 10Cadjacent in the row direction to that pixel 10C can be effectivelysuppressed.

Note that in the example illustrated in FIG. 11, the blocking structures28B and 28Bb continuously extend over multiple pixels 10C arrayed in thecolumn direction. However, the contact plug Cp8 is selectively providedto pixels 10C located at both ends, out of the multiple pixels 10Carrayed in the column direction. Thus, in a case where the blockingstructures 28B and 28Bb continuously extend over multiple pixels 10C,contact plugs Cp8 may be provided to pixels 10C located at both ends outof the multiple pixels 10C arrayed in the column direction, and contactplugs Cp8 be omitted from the remaining pixels 10C.

Pixels where the contact plugs Cp8 have been placed may be dummy pixelsplaced outside of the imaging region R1. Providing dummy pixels that arenot intended to acquire image signals, and selectively disposing thecontact plugs Cp8 in the dummy pixels enables dispersion of impuritiesfrom the contact plugs Cp8 to the semiconductor substrate 76 due toconnection of the contact plugs Cp8 to the semiconductor substrate 76 tobe avoided at the other pixels. Accordingly, occurrence of unwantedcarriers around the contact can be suppressed in pixels where thecontact plug Cp8 has been omitted. As a result, leak current issuppressed at the n-type impurity region 67 n.

One or both of the above-described well contact 62C and substratecontact 61C may be formed in the region where dummy pixels are disposed.By forming the impurity region 69 pa and impurity region 69 pbcontinuously over multiple pixels as exemplified in FIG. 11, commonvoltage can be applied in a batch to the impurity region 69 pa andimpurity region 69 pb in multiple pixels belonging to the same column byapplying voltage to the substrate contact 61C disposed in a dummy pixel.

FIG. 12 illustrates another example of the two-dimensional array of thepixels 10C. In this example, pixels 10Ca that have the same elementlayout as the example illustrated in FIG. 10, and pixels 10Cb that havea structure of a mirror image of the pixels 10Ca on a virtual axispassing through the center of the pixels 10Ca and extending parallel tothe column direction of the multiple pixels, are alternately arrayed inthe row direction of the multiple pixels. That is to say, in the columndirection of the multiple pixels, i.e., in the vertical direction of theplane of the drawing, pixels 10Ca are adjacent to pixels 10Ca, andpixels 10Cb are adjacent to pixels 10Cb.

Looking at the n-type impurity region 68 bn for example, a blockingstructure 28B is always interposed between the n-type impurity region 68bn and the n-type impurity region 67 n closest to that n-type impurityregion 68 bn in the row direction, due to employing this array ofpixels. In other words, a situation can be avoided where an n-typeimpurity region 68 bn and n-type impurity region 67 n are adjacent inthe row direction without a blocking structure 28B interposedtherebetween, among mutually adjacent pixels 10Ca and pixels 10Cb.Accordingly, the blocking structures 28Bb can be omitted. An array maybe employed where pixels 10Ca and pixels 10Cb are disposed alternatelyrepeating in the column direction instead of in the row direction, or inaddition to in the row direction.

Fourth Modification

FIG. 13 illustrates a fourth modification of the imaging deviceaccording to the first embodiment of the present disclosure. A pixel 10Xillustrated in FIG. 13 has a photoelectric conversion structure 12Aa anda photoelectric conversion structure 12Ab.

As illustrated in FIG. 13, a signal detection circuit 14Xa is connectedto the photoelectric conversion structure 12Aa, and a signal detectioncircuit 14Xb is connected to the photoelectric conversion structure12Ab. For example, the photoelectric conversion structure 12Aa andphotoelectric conversion structure 12Ab have the opposing electrode andphotoelectric conversion layer 12 b in common, but on the other hand,have pixel electrodes that are electrically independent from each other.The pixel electrode of the photoelectric conversion structure 12Aa iselectrically connected to a charge accumulation node FDa, and the signaldetection circuit 14Xa reads out to a vertical signal line 35 a signalscorresponding to signal charges generated by the photoelectricconversion structure 12Aa and stored in the charge accumulation nodeFDa. On the other hand, the pixel electrode of the photoelectricconversion structure 12Ab is electrically connected to a chargeaccumulation node FDb, and the signal detection circuit 14Xb reads outto a vertical signal line 35 b signals corresponding to signal chargesgenerated by the photoelectric conversion structure 12Ab and stored inthe charge accumulation node FDb. That is to say, the pixel 10X isconfigured to be capable of independently reading out two types ofsignals, in accordance with which of the signal detection circuit 14Xaand signal detection circuit 14Xb is used to execute readout of signals.

In the example illustrated in FIG. 13, the signal detection circuit 14Xahas a circuit configuration similar to that of the signal detectioncircuit 14C of the pixel 10C illustrated in FIG. 8, and includes thesignal detecting transistor 22, address transistor 24, reset transistor26, bandwidth control transistor 56, first capacitive element 51, andsecond capacitive element 52. In this example, the signal detectioncircuit 14Xa further includes a third capacitive element 51 a of whichone electrode is connected to the charge accumulation node FDa. Thethird capacitive element 51 a may have a capacitance value around thesame as that of the first capacitive element 51.

The signal detection circuit 14Xa also has a feedback circuit 16Xa forfeedback of part or all of the output signals of the signal detectingtransistor 22. Note however, that a feedback line 53 a connected to oneof the source and drain of the bandwidth control transistor 56 isconnected to the source of the signal detecting transistor 22. That isto say, in the feedback circuit 16Xa, the output of the signal detectingtransistor 22 itself is used as the reference voltage for resetting.

This circuit configuration also enables a feedback loop to be formedwhere part or all of the output signals of the signal detectingtransistor 22 are fed back electrically, and the effects of kTC noisethat occurs when the reset transistor 26 and bandwidth controltransistor 56 go off can be reduced. Moreover, the inverting amplifier50 has been omitted in comparison with the example in FIG. 8, so noisecancellation using feedback can be implemented in increments of pixels10X. Details of noise cancellation in increments of pixels usingfeedback is described in Japanese Unexamined Patent ApplicationPublication No. 2016-127593, for example. Japanese Unexamined PatentApplication Publication No. 2016-127593 is incorporated herein byreference in its entirely, for reference.

The signal detection circuit 14Xa further has a protection transistor 55in this example. The drain or source of the protection transistor 55,and the gate, are connected to the charge accumulation node FDa betweenthe gate of the signal detecting transistor 22 and the photoelectricconversion structure 12Aa. The one of the drain and source of theprotection transistor 55 that is not connected to the photoelectricconversion structure 12Aa is connected to a power line 57 that receivessupply of a predetermined power source when the imaging device 100A isoperating, by being connected to a power source that is omitted fromillustration.

On the other hand, looking at the signal detection circuit 14Xb havingelectrical connection with the photoelectric conversion structure 12Ab,the signal detection circuit 14Xb includes a second signal detectingtransistor 22 b having a gate connected to the photoelectric conversionstructure 12Ab, an address transistor 24 b connected between the signaldetecting transistor 22 b and the vertical signal line 35 b, a resettransistor 26 b connected between the photoelectric conversion structure12Ab and a feedback line 53 b, and a second protection transistor 55 b.The gate of the reset transistor 26 b is connected to the reset signalline 36 b, and the vertical scanning circuit 42, for example, controlson and off of the reset transistor 26 b by control of the potential atthe reset signal line 36 b. The drain or source of the protectiontransistor 55 b and the gate thereof are connected to a chargeaccumulation node FDb between the gate of the signal detectingtransistor 22 b and photoelectric conversion structure 12Ab, and the oneof the drain and source of the protection transistor 55 b that is notconnected to the photoelectric conversion structure 12Ab is connected tothe power line 57, in the same way as the above-described protectiontransistor 55.

An address signal line 34 b is connected to the gate of the addresstransistor 24 b of the signal detection circuit 14Xb. The address signalline 34 b is connected to the vertical scanning circuit 42 for example,and the vertical scanning circuit 42, controls on and off of the addresstransistor 24 b by control of the potential at the address signal line34 b. That is to say, according to the circuit exemplified in FIG. 13,one of the signal detection circuits 14Xa and 14Xb can be selected andsignals corresponding to the amount of charge accumulated in the chargeaccumulation node FDa or signals corresponding to the amount of chargeaccumulated in the charge accumulation node FDb can be selectively readout.

The signal detection circuit 14Xb includes a feedback circuit 16Xb.Accordingly, due to formation of a feedback loop where part or all ofthe output signals of the signal detecting transistor 22 b are fed backelectrically, the kTC noise that occurs when the reset transistor 26 bgo off can be reduced, in the same way as with the signal detectioncircuit 14Xa.

The signal detection circuit 14Xb has, as a part thereof, a capacitiveelement 52 b having a relatively large capacitance value by beingprovided within the pixel 10X in a MIM structure, for example. Asillustrated in FIG. 13, one electrode of the capacitive element 52 b isconnected to the charge accumulation node FDb, and the other electrodeis connected to the sensitivity adjustment line 54. The capacitiveelement 52 b connected to the charge accumulation node FDb has functionsof increasing the capacitance value of the overall charge accumulationregion that accumulates signal charges.

According to the circuit exemplified in FIG. 13, signals in accordancewith the amount of charge accumulated in the charge accumulation nodeFDa and signals in accordance with the amount of charge accumulated inthe charge accumulation node FDb can be selectively read out, asdescribed above. The capacitive element 52 b that has a relatively largecapacitance value is connected to the charge accumulation node FDb inthe signal detection circuit 14Xb, and accordingly, more signal chargescan be stored, which is advantageous in shooting in a high-luminanceenvironment, for example. On the other hand, the signal detectioncircuit 14Xa includes, as a part thereof, the first capacitive element51 connected in parallel to the reset transistor 26, and can executenoise cancellation more effectively while suppressing increase in thecapacitance value of the overall charge accumulation region.Accordingly, this is particularly advantageous in shooting with highsensitivity. Thus, an arrangement may be made where two signal detectioncircuits are provided within one pixel, and readout of signals isexecuted via the signal detection circuit of these that is more suitablefor the shooting scene. The term “pixel” in the present specificationindicates, for example, a unit configuring a repetitive structure in theimaging region R1, and is not restricted to a structure including asingle signal detection circuit but rather may include two or moresignal detection circuits.

FIG. 14 illustrates an example of the layout of the elements in thepixel 10X illustrated in FIG. 13, and FIG. 15 illustrates an example ofa two-dimensional array of the pixel 10X illustrated in FIG. 13. InFIGS. 14 and 15, dotted lines indicate the general positions of impurityregions 69 pa and impurity regions 69 pb.

Of the four pixels illustrated in FIG. 15, a pixel 10Xa located to thelower right has a structure of a mirror image of the pixel 10X on avirtual axis passing through the center of the pixel 10X and extendingparallel to the column direction of the multiple pixels. Of the fourpixels illustrated in FIG. 15, a pixel 10Xb located to the upper rightand a pixel 10Xc located to the upper left have a structure of a mirrorimage of the pixel 10X and pixel 10Xa on a virtual axis passing throughthe center of the pixel 10X and extending parallel to the row directionof the multiple pixels. In the fourth modification, the imaging regionR1 can be formed from a repetition where a group of these four pixels10X and 10Xa through 10Xc are an increment.

In the example illustrated in FIG. 14, the blocking structure 28B isdisposed at the general middle of the pixel 10X, and the signaldetection circuits 14Xa and 14Xb are disposed in the pixel 10Xsurrounding the blocking structure 28B. In this example, multiple n-typeimpurity regions including such as the n-type impurity region 68 bn arelocated on the periphery of the impurity region 69 n of the blockingstructure 28B. Accordingly, the impurity region 69 pa and impurityregion 69 pb of the blocking structure 28B are provided in the pixel 10Xsurrounding the impurity region 69 n here. Although two regions areillustrated in FIG. 14 as if a boundary exists between the impurityregion 69 pa and the impurity region 69 pb, the impurity region 69 paand impurity region 69 pb are part of the pixel isolation region 69, andno such clear boundary exists therebetween, as described above.

The impurity region 69 pa and impurity region 69 pb of the blockingstructure 28B is located between the n-type impurity region 68 bn andthe n-type impurity region 67 n serving as the signal detection circuit14Xa side charge accumulation region in this example, as schematicallyillustrated in FIG. 14. Accordingly, inflow of excess charges from then-type impurity region 68 bn to the n-type impurity region 67 n of thesignal detection circuit 14Xa can be suppressed by the blockingstructure 28B. Placing the blocking structure 28B or blocking structure28A so as to be interposed between the n-type impurity region 67 n ofthe signal detection circuit 14Xa at the high-sensitivity side wheredemand for noise suppression is relatively strict, and the n-typeimpurity region 68 bn, enables deterioration in image quality due toleak current to be effectively suppressed. It can be understood fromFIG. 14 that while the feedback lines 53 a and 53 b are illustrated inthe form of lines in FIG. 13, the structure to electrically connect thesource of the signal detecting transistor 22 to the bandwidth controltransistor 56 and the structure to electrically connect the source ofthe signal detecting transistor 22 b to the reset transistor 26 b arenot restricted to the form of lines.

Second Embodiment

FIG. 16A schematically illustrates an exemplary device structure of apixel 10E that an imaging device according to a second embodiment of thepresent disclosure has. The primary point of difference between thepixel 10A described with reference to FIG. 3A and the pixel 10Eillustrated in FIG. 16A is that the pixel 10E has a blocking structure28E instead of the blocking structure 28A. Note that in this example,the pixel 10E has a semiconductor substrate 60B instead of thesemiconductor substrate 60A in comparison with the pixel 10A.

In comparison with the blocking structure 28A illustrated in FIG. 3A,the blocking structure 28E illustrated in FIG. 16A has, instead of theimpurity region 69 n, impurity region 69 pa, and impurity region 69 pb,an impurity region 69 p, and a p-type impurity region 69 b located inthe impurity region 69 p, between the n-type impurity region 68 bn andn-type impurity region 67 n. The impurity region 69 p here is part ofthe pixel isolation region 69, and typically is provided in the p-typesemiconductor layer 65 p in the form of a p-type diffusion region. Inthis example, the n-type impurity region 68 bn and the n-type impurityregion 67 n are also located in the p-type semiconductor layer 65 p, asillustrated in FIG. 16A.

The impurity region 69 b located in the impurity region 69 p is a p-typediffusion region, and has a concentration of impurity that is higherthan the impurity region 69 p by an order of around one digit. Theconcentration of impurity of the impurity region 69 b may be around3×10¹⁹ cm⁻³ for example. At least part of the impurity region 69 b inthe blocking structure 28E is located on the surface of thesemiconductor substrate 60B, in the same way as the impurity region 69 nin the blocking structure 28A.

The element layout when viewing the pixel 10E from the normal directionof the semiconductor substrate 60B may be the same as the element layoutexemplified in FIG. 10, with the blocking structure 28B replaced by theblocking structure 28E. That is to say, at least part of the impurityregion 69 b where the concentration of p-type impurity has been maderelatively high is located between the n-type impurity region 68 bnserving as the drain region of the signal detecting transistor 22 andthe n-type impurity region 67 n serving as the charge accumulationregion.

In the first embodiment described above, the blocking structure isformed by the impurity region 69 n having the same conductivity type asthe conductivity type of the gate electrode of the transistor making upthe signal detection circuit. Conversely, the blocking structure 28E isformed by the p-type impurity region 69 b having a conductivity typethat is of inverse polarity as the gate electrode of the transistor. Inthis way, the same effects as those of the blocking structure 28A in thefirst embodiment can be obtained by an arrangement where a impurityregion 69 p, for example, is disposed between the n-type impurity region68 bn and the n-type impurity region 67 n serving as a chargeaccumulation region, and the impurity region 69 b having an even higherconcentration of impurity is formed in the impurity region 69 p.

Note that in the blocking structure 28A according to the firstembodiment, the impurity region 69 pa and impurity region 69 pb ofdifferent conductivity type from the impurity region 69 n are disposedin the semiconductor substrate 60A so as to sandwich the impurity region69 n therebetween. That is to say, no p-type impurity region havingrelatively high concentration of impurity is disposed below the impurityregion 69 n. In comparison with this, in the blocking structure 28Eillustrated in FIG. 16A, the impurity region 69 b is surrounded by theimpurity region 69 p having relatively high concentration of impurity.According to this arrangement, minority carriers can be suppressed frompassing around from below the impurity region 69 b, and the number ofminority carriers arriving at the n-type impurity region 67 n serving asthe charge accumulation region can be suppressed, as compared to a casewhere an n-type impurity region is disposed sandwiching the impurityregion 69 b.

By forming the impurity region 69 b having relatively high concentrationof impurity between the n-type impurity region 68 bn and the n-typeimpurity region 67 n, electrons generated at the n-type impurity region68 bn and heading toward the n-type impurity region 67 n can beeliminated at the position of the impurity region 69 b by recombinationwith majority carriers. That is to say, contamination of the n-typeimpurity region 67 n by excess charges from the n-type impurity region68 bn can be suppressed, yielding an effect of suppressing leak current.The blocking structure is formed by placing a region that has commonconductivity type and relatively high concentration of impurity in thep-type impurity region 69 p, instead of forming the blocking structureby placing an n-type impurity region with relatively high concentrationof impurity, between two p-type impurity regions disposed apart fromeach other. Accordingly, the number of p-n junctions in thesemiconductor substrate 60B can be reduced. Effects of reduction inoccurrence of charges that are the cause of leak current areanticipated.

Modifications

FIG. 16B schematically illustrates the device structure of a pixel thatthe imaging device according to a first modification of the secondembodiment has. In a pixel 10Es exemplified in FIG. 16B, thesemiconductor substrate 60B has a p-type impurity region 63 pr on then-type semiconductor layer 62 n. The concentration of impurity of thep-type impurity region 63 pr is higher than that of the p-typesemiconductor layer 65 p, and may be around 3×10¹⁸ cm⁻³ or higher, forexample. In this example, the p-type impurity region 63 pr isselectively formed at a region overlapping the blocking structure 28Eand the n-type impurity region 67 n serving as a charge accumulationregion in the semiconductor substrate 60B, in plan view.

The p-type impurity region 63 pr typically does not exist directlybeneath the n-type impurity region 68 bn, as schematically illustratedin FIG. 16B. According to studies made by the present inventors,disposing the p-type impurity region 63 pr avoiding the region of thesemiconductor substrate 60B that overlaps the n-type impurity region 68bn in plan view tends to result in the n-type semiconductor layer 62 ndirectly beneath the n-type impurity region 68 bn spreading toward then-type impurity region 68 bn. If the boundary between the n-typesemiconductor layer 62 n and p-type semiconductor layer 65 p come nearto the n-type impurity region 68 bn, electrons occurring at the p-njunction between the n-type impurity region 68 bn and the surroundingsthereof more readily move to the n-type semiconductor layer 62 n. As aresult, the number of minority carriers moving from the n-type impurityregion 68 bn toward the n-type impurity region 67 n decreases, and theeffects of leak current suppression can be obtained.

In the configuration exemplified in FIG. 16B, the p-type impurity region63 pr does not exist directly below the n-type impurity region 68 aneither. Placing the p-type impurity region 63 pr avoiding a regionoverlapping the n-type impurity region 68 an in plan view enables then-type semiconductor layer 62 n to expand toward the n-type impurityregion 68 an directly below the n-type impurity region 68 an.Accordingly, effects of suppressing contamination of the n-type impurityregion 67 n by electrons generated at the p-n junction between then-type impurity region 68 an and the surroundings thereof can beobtained, in the same way as the case of forming the p-type impurityregion 63 pr avoiding directly below the n-type impurity region 68 bn.Note that the p-type impurity region 63 pr exemplifies a third impurityregion.

FIG. 17 schematically illustrates the device structure of a pixel thatthe imaging device according to a second modification of the secondembodiment has. A pixel 10 OF illustrated in FIG. 17 has a blockingstructure 28F instead of the blocking structure 28E, in comparison withthe pixel 10Es illustrated in FIG. 16B. The blocking structure 28Ffurther includes the contact plug Cp8 connected to the impurity region69 b, as illustrated in FIG. 17. The contact plug Cp8 here is apolysilicon plug that has been imparted conductivity by being doped by ap-type impurity. The contact plug Cp8 is connected to the voltage line38, in the same way as the example described with reference to FIG. 5.The voltage line 38 has no electrical connection with any of the addresssignal line 34, reset signal line 36, and conductive structure 89, inthe same way as the examples illustrated in FIGS. 5 and 9.

FIG. 18 schematically illustrates an example of electrical connectionbetween a pixel 10 OF and the voltage supply circuit 48. The blockingstructure 28F has a configuration where a predetermined voltage can beapplied to the impurity region 69 b via the voltage line 38. A desiredvoltage can be applied to the n-type semiconductor layer 62 n as well inthis example, by the second voltage supply circuit 48 b being connectedto the well contact 62C.

When the imaging device 100A is operating, the voltage supply circuit 48supplies voltage of 0 V, for example, to the impurity region 69 b. Onthe other hand, voltage of 0.5 V is applied from the voltage supplycircuit 48 b to the n-type semiconductor layer 62 n. That is to say, thepotential of the impurity region 69 b and the potential of the n-typesemiconductor layer 62 n can be independently controlled. In theconfiguration exemplified in FIG. 18, the predetermined voltage of 0 V,for example, is directly applied to the p-type impurity region 69 b bythe voltage line 38 having been connected to the impurity region 69 b,but an arrangement may be made where the voltage line 38 is connected tothe above-described substrate contact 61C, and voltage is applied to theimpurity region 69 b via the supporting substrate 61, p-type region 64,p-type semiconductor layer 65 p, and impurity region 69 p. Note however,that the arrangement where the voltage line 38 is connected to theimpurity region 69 b without going through the p-type semiconductorlayer 65 p and so forth, as illustrated in FIG. 18, is more advantageousin that voltage can be supplied to the impurity region 69 b whileremoving the effects of resistance components from the substrate contact61C up to the impurity region 69 b.

Further, voltage applied to the p-type impurity region 69 b may besupplied in common to the impurity region 69 p via the substrate contact61C. Fixing the potential of the impurity regions 69 p and 69 b byapplying voltage from outside of the pixel 10F can suppresscontamination of the n-type impurity region 67 n by minority carrierseven more effectively. Application of voltage to the impurity regions 69p and 69 b may be executed by a single voltage supply circuit, e.g., thevoltage supply circuit 48. Application of voltage does not have to beexecuted perpetually, and it is sufficient to be selectively executed incharge accumulation periods.

Note that in the configuration exemplified in FIG. 17, a predeterminedvoltage is applied from the voltage line 38 to the impurity region 69 bvia the contact plug Cp8, but an arrangement may be made where thecontact plug Cp8 is omitted and a metal line is connected to theimpurity region 69 b. In this case, it is advantageous for the impurityregion 69 b to have a concentration of impurity around 3×10¹⁹ cm⁻³ orhigher, for example.

Third Embodiment

FIGS. 19 and 20 illustrate an imaging device according to a thirdembodiment of the present disclosure. FIG. 19 illustrates an example ofthe layout of elements in a pixel 10G that the imaging device accordingto the third embodiment has, and FIG. 20 illustrates an exemplarycircuit configuration of the pixel 10G illustrated in FIG. 19.

The pixel 10G illustrated in FIGS. 19 and 20 has a photodiode 12B as thephotoelectric converter 12. In a case of applying the photodiode 12Binstead of the photoelectric conversion structure 12A, the accumulationcontrol line 31 illustrated in FIG. 2 is omitted. The point of one ofthe drain and source of the reset transistor 26 being connected to thecharge accumulation node FD is the same as the configuration illustratedin FIG. 2. Note however, that the power source wiring 32 is connected tothe other of the drain and source of the reset transistor 26 here.

The pixel 10G includes a signal detection circuit 14G connected to thephotodiode 12B. The signal detection circuit 14G further includes atransfer transistor 29, which is connected between the gate of thesignal detecting transistor 22 and the photodiode 12B, as compared tothe signal detection circuit 14A of the above-described pixel 10A. Atransfer signal line 39 is connected to a gate electrode 29 e of thetransfer transistor 29. The transfer signal line 39 has connection withthe vertical scanning circuit 42 for example, and the potential thereofis controlled by the vertical scanning circuit 42. The vertical scanningcircuit 42 can control the timing of transferring signal chargesgenerated at the photodiode 12B to the charge accumulation node FD, byon and off control of the transfer transistor 29.

In this example, the charge accumulation node FD is a node where thegate electrode 22 e of the signal detecting transistor 22 connects tothe photodiode 12B. The charge accumulation node FD includes as partthereof the n-type impurity region 67 n formed on the semiconductorsubstrate 60A, in the same way as the examples described above. In theconfiguration exemplified in FIG. 19, the p-type impurity region 66 pwith relatively low concentration of impurity is located between thegate electrodes 26 e and 29 e in plan view. The n-type impurity region67 n is located in the p-type impurity region 66 p.

The blocking structure 28A is disposed between the n-type impurityregion 67 n and the n-type impurity region 68 bn in the exampleillustrated in FIG. 19 as well. Accordingly, the unwanted minoritycarriers moving toward the n-type impurity region 67 n can be suppressedfrom contaminating the n-type impurity region 67 n by the blockingstructure 28A. In this example, the impurity region 69 pa and theimpurity region 69 pb of the blocking structure 28A are provided in thepixel 10G surrounding the impurity region 69 n, in the same way as inthe example described referencing FIGS. 14 and 15. It is needless to saythat any of the above-described blocking structures 28B, 28E, and 28Fmay be applied instead of the blocking structure 28A.

EXAMPLES

The effects of suppressing leak current by providing the blockingstructure in a pixel were verified by simulation. A generalcommercially-available device simulator was used for the simulation.

FIG. 21 schematically illustrates a model used for simulation. Thedistribution of concentration of n-type impurities is also illustratedin FIG. 21. The magnitude of the leak current was evaluated by assuminga structure the same as that of the pixel 10B illustrated in FIG. 5, andcalculating what percentage of electrons generated at the positionindicated by the black dot GR in FIG. 21 would reach the n-type impurityregion 67 n. The heavy dashed line in FIG. 21 represents the position ofthe p-n junction, and the distance indicated by double-headed arrow s1,the distance indicated by double-headed arrow s2, and the distanceindicated by double-headed arrow s3, were set to 90 nm, 390 nm, and 50nm, respectively. The potential of the n-type impurity region 67 n andn-type impurity region 68 bn are fixed to 0.5 V and 3.3 V, respectively.Analysis was performed assuming a state where voltage of 0.5 V isapplied to the blocking structure 28B and n-type semiconductor layer 62n.

First Example

FIGS. 22 and 23 illustrate simulation results relating to a firstexample assuming basically the same structure as that of the pixel 10Billustrated in FIG. 5. FIG. 22 indicates the calculation resultsrelating to potential at each part, and FIG. 23 illustrates thecalculation results relating to current density at each part.Hereinafter, in the drawings, the heavy solid line indicates theposition of the p-n junction, and the rectangle Ct indicates theposition of a substrate contact.

Second Example

Next, analysis was performed assuming, as a sample for a second example,a configuration where the p-type semiconductor layer 63 p covers almostthe entire face of the n-type semiconductor layer 62 n as in the exampledescribed with reference to FIG. 3A, i.e., a configuration where thep-type semiconductor layer 63 p is disposed instead of the p-typesemiconductor layer 63 ps having an opening directly beneath theimpurity region 69 n. FIG. 24 indicates the calculation results relatingto potential at each part of the sample for the second example, and FIG.25 illustrates the calculation results for current density at each partof the sample for the second example.

First Comparative Example

Next, a configuration where the blocking structure 28B was removed fromthe sample of the second example was assumed as a sample for a firstcomparative example, and analysis was performed. FIG. 26 indicates thecalculation results relating to potential at each part of the sample forthe first comparative example, and FIG. 27 illustrates the calculationresults relating to current density at each part of the sample for thefirst comparative example.

FIG. 28 illustrates calculation results of the percentage of inflow ofcharges to the n-type impurity region 67 n out of the charges generatednear the n-type impurity region 68 bn. In FIG. 28, the calculationresults relating to the first example are plotted to the far right, andthe calculation results relating to the second example are plotted atthe middle. The calculation results relating to the first comparativeexample are plotted to the far left in FIG. 28.

It can be seen from the calculation results relating to the first andsecond examples and the calculation results relating to the firstcomparative example in FIG. 28 that the leak current can be reduced byan order of around five digits by providing the blocking structure inthe pixel. Also, comparing the calculation results relating to the firstexample and the calculation results relating to the second example showsthat in particular, providing an opening in the p-type semiconductorlayer 63 ps and disposing the p-type impurity region 66 p withrelatively low concentration of impurity in the opening, as in the pixel10B illustrated in FIG. 5, enables the leak current to be furtherreduced by an order of around two digits.

Next, the effects of reduced leak current by placing the p-type impurityregion 66 p directly below the impurity region 69 n making up theblocking structure 28B were verified by calculating the magnitude ofelectric field at each part with regard to the samples of the firstexample and second example. FIG. 29 illustrates calculation resultsrelating to the electric field at each part of the sample in the firstexample, and FIG. 30 illustrates calculation results relating to theelectric field at each part of the sample in the second example.

Looking closely at the region between the impurity region 69 n, and theportion of the n-type semiconductor layer 62 n that is located directlybeneath the impurity region 69 n, it can be seen from comparing FIGS. 29and 30 that the p-n junction at the boundary between the n-typesemiconductor layer 62 n and the upper layer thereof is generally flatin the sample according to the second example, while the p-n junctionbetween the n-type semiconductor layer 62 n and the upper layer thereofbulges upwards toward the impurity region 69 n directly beneath theimpurity region 69 n in the sample according to the first example.Accordingly, while there is a relatively large region where the electricfield is small, directly beneath the impurity region 69 n in the samplein the second example, as indicated by the heavy dotted lines in FIG.30, the distance between these heavy dotted lines is narrow in thesample in the first example.

This suggests that the path of movement of charges heading from then-type impurity region 68 bn toward the n-type impurity region 67 n isnarrowed directly beneath the impurity region 69 n in the sample in thesecond example. That is to say, by selectively lowering theconcentration of impurity at the portion of the p-type semiconductorlayer 63 ps located directly beneath the impurity region 69 n narrowsthe path of movement of charges between the n-type impurity region 68 bnand n-type impurity region 67 n. Accordingly, charges generated at then-type impurity region 68 bn and the periphery thereof that move throughthe semiconductor substrate advance toward the impurity region 69 n orthe n-type semiconductor layer 62 n following the potential gradient,and are absorbed at the impurity region 69 n or n-type semiconductorlayer 62 n. That is to say, inflow of unwanted minority carriers to then-type impurity region 67 n is blocked at the position of the impurityregion 69 n, so unwanted current less readily flows into the n-typeimpurity region 67 n serving as the charge accumulation region, andeffects of suppressed leak current can be obtained.

As described above, according to embodiments of the present disclosure,the effects of leak current can be suppressed, and accordingly animaging device capable of imaging with high image quality can beprovided. Note that the conductivity types of impurity regions in thesemiconductor substrate are not restricted to the arrangements in theabove-described examples, and that configurations may be made wheren-type and p-type are inverted. Also note that the transistors describedabove, such as the signal detecting transistor 22, address transistor24, reset transistor 26, and so forth, may be N-channel MOS devices ormay be p-channel MOS devices. These transistors do not have to be allN-channel MOS devices or all p-channel MOS devices. In a case of usingN-channel MOS devices for the transistors in the pixel, and usingelectrons as the signal charge, it is sufficient to invert the layout ofsources and drains of the transistors.

According to embodiments of the present disclosure, an imaging devicethat can suppress effects of leak current and take high quality imagesis provided. The imaging device according to the present disclosure isuseful in, for example, image sensors, digital cameras, and so forth.The imaging device according to the present disclosure can be used inmedical cameras, robotic cameras, security cameras, cameras installed invehicles and used, and so forth.

What is claimed is:
 1. An imaging device, comprising: a photoelectricconverter that generates a signal charge by photoelectric conversion oflight; a semiconductor substrate that includes a first semiconductorlayer containing an impurity of a first conductivity type and animpurity of a second conductivity type different from the firstconductivity type; and a first transistor that includes, as a source ora drain, a first impurity region of the second conductivity type in thefirst semiconductor layer, wherein the first semiconductor layerincludes: a charge accumulation region that is an impurity region of thesecond conductivity type, the charge accumulation region beingconfigured to accumulate the signal charge; and a blocking structurethat is located between the charge accumulation region and the firsttransistor, the blocking structure includes: a second impurity region ofthe first conductivity type, a third impurity region of the secondconductivity type, and a fourth impurity region of the firstconductivity type, and at a surface of the first semiconductor layer,the second impurity region, the third impurity region, and the fourthimpurity region, are arranged in that order in a first direction fromthe first impurity region toward the charge accumulation region.
 2. Theimaging device according to claim 1, wherein the semiconductor substrateincludes a supporting substrate including an impurity of the firstconductivity type, and a second semiconductor layer that is locatedbetween the supporting substrate and the first semiconductor layer, thesecond semiconductor layer including an impurity of the secondconductivity type.
 3. The imaging device according to claim 2, whereinthe semiconductor substrate further includes a third semiconductor layerthat is located between the first semiconductor layer and the secondsemiconductor layer, the third semiconductor layer including an impurityof the first conductivity type, the third semiconductor layer has anopening that overlaps the third impurity region in a plan view, and aconcentration of impurity of the first conductivity type in a regionlocated in the opening is lower than a concentration of impurity of thefirst conductivity type in the third semiconductor layer.
 4. The imagingdevice according to claim 1, further comprising a voltage supply circuitconfigured to apply, to the third impurity region, a first voltage thatis inverse bias with regard to the first semiconductor layer, or asecond voltage that is a same voltage as the first semiconductor layer,in a period in which the signal charge is accumulated in the chargeaccumulation region.
 5. The imaging device according to claim 4, whereina third voltage that is different from the first voltage, or the secondvoltage that is 0 V, is applied to the second impurity region and thefourth impurity region via the first semiconductor layer, in the period.6. The imaging device according to claim 5, wherein the third voltage isless than the first voltage.
 7. The imaging device according to claim 4,wherein a same voltage is applied to the third impurity region and thesecond semiconductor layer in the period.
 8. The imaging deviceaccording to claim 1, further comprising: a second transistor includingthe charge accumulation region as one of a source and a drain, wherein asame voltage is applied to the third impurity region and the other ofthe source and the drain of the second transistor.
 9. The imaging deviceaccording to claim 1, wherein the second impurity region and the fourthimpurity region are a single continuous impurity region surrounding thethird impurity region.
 10. An imaging device, comprising: aphotoelectric converter that generates a signal charge by photoelectricconversion of light; a semiconductor substrate that includes a firstsemiconductor layer containing an impurity of a first conductivity typeand an impurity of a second conductivity type different from the firstconductivity type; and a first transistor that includes, as a source ora drain, a first impurity region of the second conductivity type in thefirst semiconductor layer, wherein the first semiconductor layerincludes: a charge accumulation region that is an impurity region of thesecond conductivity type, the charge accumulation region beingconfigured to accumulate the signal charge; and a blocking structurethat is located between the charge accumulation region and the firsttransistor, and the blocking structure includes: a second impurityregion of the first conductivity type; and a third impurity region ofthe first conductivity type, that is located in the second impurityregion, a part of the third impurity region being located on a surfaceof the first semiconductor layer, a concentration of impurity of thefirst conductivity type in the third impurity region being higher than aconcentration of impurity of the first conductivity type in the secondimpurity region.
 11. The imaging device according to claim 10, whereinthe semiconductor substrate includes a supporting substrate including animpurity of the first conductivity type, and a second semiconductorlayer that is located between the supporting substrate and the firstsemiconductor layer, the second semiconductor layer including animpurity of the second conductivity type.
 12. The imaging deviceaccording to claim 11, wherein the semiconductor substrate furtherincludes a fourth impurity region that is located between the firstsemiconductor layer and the second semiconductor layer, the fourthimpurity region including an impurity of the first conductivity type,and a concentration of impurity of the first conductivity type in thefourth impurity region is higher than a concentration of impurity of thefirst conductivity type in the first semiconductor layer.
 13. Theimaging device according to claim 12, wherein the fourth impurity regiondoes not overlap the first impurity region in a plan view.
 14. Theimaging device according to claim 12, further comprising: a secondtransistor including the charge accumulation region as one of a sourceand drain, wherein the fourth impurity region does not overlap the otherof the source and the drain of the second transistor in a plan view. 15.The imaging device according to claim 10, further comprising: a voltagesupply circuit configured to apply a first voltage to the third impurityregion, in a period in which the signal charge is accumulated in thecharge accumulation region.
 16. The imaging device according to claim15, wherein a same voltage as the first voltage is applied to the secondimpurity region via the supporting substrate.